Notes from – Aquaponic Gardening

Chapter 1 What is aquaponics

This is an environmentally friendly, natural food-growing myth that harnesses the best attributes of aquaculture and hydroponics without the need to discard any water or filtrate or add chemical fertiliser

By combing the two systems, aquaponic transfers much of the rsponosibil9ityu for reaching equilibrium between the filtration of the fish waste and the nutrient need sof the plant to Mother Nature

Hydro ponics ‘water working’

NFT – Nutrient Film Technique DWC – Deep-water culture or raft

Aquaponics an improvement on hydroponics:

 Use less expensive fish feed than chemicals  Never dump the nutrient solution –  Maintaining aquaponics is easier – dynamic equilibrium  Aquaponics is more productive once filter is established  Completely organic

P 7 blog on current trends in aquaculture and what aquaponics could offer it

Chapter 2 – Global Perspective

Bad news – Headings p9 -25

 Future food economics: increased demand  Population Growth  Increased standards of living for developing countries  Future food economics, decreased supply  Petroleum use in agriculture  Water use in agriculture  Climate change & agriculture  Deforestation  Overfishing the oceans

Good news

 Petroleum use in aquaponics compared with agriculture  Experience in using renewables & saving energy  No need to work soil – tractors  No need to weed  No fertilisers  Aquaponics can be carried out any where – local food for local communities – less food miles  Water use in aquaponics v agriculture  No irrigation  Far less water loss  No need to dump nutrient soln – like hydroponics Aquaponics is not completely human managed but is a joint venture with nature – each partner doing what it is best at.  You should never have to discharge water – like in nature where there is no pollution.

1 Climate change: aquaponics V aquaculture  Much less use of petroleum and a potential to develop much more – fish don’t produce methane or can you over fertilise your aquaponics system  Aquaponics can produce: 50,000lbs of fish to 100000 of veg per acre, where one cow needs 8 acres – eg aquaponics can produce 35,000lbs of flesh per year compared to 75lbs of grass fed beef for the same area

Aquaponics v aquaculture

“In an aquaponics system, nature plays the lead role and the successful farmer conducts rather than dictates”

Increasingly intensive aquaculture techniques will be needed to supply fish needs for the future, but such systems produce toxic wastes – aquaponics can be the solution for turning a problem into an opportunity but will require fish farmers to become horticulturists as well – which is how it is in nature anyway. We are really just re-inventing the wheel.

Chapter 3 Home food production

Earth smart gardening  Organic not fertilisers,  Use 10% of water  Waste is a nutrient  Weed and ‘dirt’ free  Locally grown

Convenient gardening  Waist high  Weed & dirt free  No water  No fertilising  Located anywhere

Year round gardening  Move system inside in the winter  Locate small systems inside all the time  Use a green house with appropriate insulation and heating etc

Growing your own fish:  Convenient  Safe  Fresh  Food independence  Fun

Section 2 The plan

Chapter 4

Before you start Questions – why, where, when, who, how

Why? – and important question to bear in mind all the time Reduce food bills Want to start a business Where Garden, basement etc What does the rest of the family feel about it?

2 When do you want to start and for how long

Who will be involved and be responsible

Hardware – the infrastructure which needs built first Software – the living part

Chapter 5 System location & environment

4 options

 Grow for 3 seasons of the year and shut down  Grow indoors  Grow outdoors in summer and move in the winter  Grow in a greenhouse

3 seasons  Need to start as soon as possible when there is no risk of frost  Problem of fish not being big enough before shut down  Issues of keeping fish and plant alive during the winter  Issues concerning the filter at 18oC bacteria growth rates is decreased by 50% than if temp is 25 – 30oC

Indoors  Considerations for indoors:  Weight  Humidity e.g condensation  Water spillage  Light – heat, power, additional effort  Sound

Mitigation by having a grow room.

Outdoors in the summer bring in in the winter  Logistics and the issues considered above.

Erect a greenhouse

Greenhouse gives you total control:  Light control  Water on tap  Special oasis – sanctuary

Considerations for greenhouses:  Insulate down to the frost line on the base  Insulate the north wall  Ideally double layer of glass to reduce heat loss – option to use recycled materials  Fish tank can act as a heat sink therefore position appropriately.  Built in power and water  Reliable power and contingency back up  Water heating need 240w to raise 380l 0.56oC with 400 w heater this will do this in 36mins  Fish produce CO2 which the plants need

Temperate climates

Lights

3 Either for indoors or increase light during the winter in a green house.

Factors to consider:

 Duration  Spectrum - aim for ‘grow light, plant light, daylight spectrum’ must have the red and blue spectrum  Canopy penetration – needs of a tomato plant is different from a lettuce  Heat Lights can produce heat – pros and cons  Energy input for light output  Cost

Fluorescent lighting T 5 – Number is the diameter

Pros: slim, low heat, broad spectrum, aethetics Cons: penetration 45cms, performance drops off after 6 months

High Intensity Discharge

High Pressure Sodium – most red spectrum for vegetative growth Metal Halide – blue spectrum for mature / fruiting stage Pros: very intensive good penetration, with switchable ballast can switch from HPS to MH Cons: expensive, use more power and expel a lot heat

LED lighting

1 x 400watt HPS = 10 x 54 watt T5 = 5.5 x 125watt Fluoresent lamp= 42 40watt fluorescent = 84 60watt incandescent light bulb

Chapter 6 System Design

1. Basic Flood and Drain 2.

Grow Bed

Fish tank

Simplest design – circulation especially if 1: 1 fish to grow bed . if 1: 2 then can have a problem of large fluctuation in fish tank level. Can use a sequence valve which allows for tanks to be filled sequentially.

3. Add a sump CHOP – Constant height one pump

Grow Bed Grow Bed Fish tank

Sump & pump

Pros: Only one pump, fewer areas to go wrong & less energy Cons: growbed must be absolutely level, fish tank must be above the grow beds, danger of sump pump – pumping dry,

4 Alternative is a CHOP 2 Here you have a double loop water going to the fish tank & grow beds at the same time and then return to the sump

Grow bed

Fish Tank & Pump Sump & Pump

Pump can work continuously or by float switch from sump to fish. Pros: fish tank can be any height Cons: 2 pump, costs, switching on/off pump shortens pump life

Barrel-ponics

Consists of flood tank, grow bed, fish tank Pump water from fish tank to flood tank – to a certain level at which point a small siphon starts to fill a counterweight, when heavy enough pulls a valve to flood the grow beds. When flood tank is empty, siphon stops. Nutrient slowly return to the fish tank and the cycle starts again.

Pros: use recycled materials, flood characteristics are easily changed, materials are widely available, pump runs continuously, Cons: not attractive and complex support framing

Hybrid system

DWC & NFT require solids filtration there fore having a combination of media bed and DWC or NFT – get the perfect balance.

Basic flood CHOP 2 pump Barrel- Hybrid & drain ponics Ease of H M M-L M L assembly Ease of H M M M L maintenance Ease of M M M M H harvest Expandablity M H H L Depends on pipe config Complex/ L M – 1 float H – 2 float M – 1 float H – 2 risk of valve valves valve different problems styles Power use L L M L M

Pros for media  Three filter functions – physical, biological & chemical or mineralisation  All in one component therefore simple  Good plant support  Cost is lower due to fewer components -?  Easier to understand and learn  Basic is simple 1:1  CHOP to expand

5 Section 3 Hardware

Chapter 7 Growbeds & fish tanks

Fish feed > Fish stocking density>Fish waste>Bio filtration>Grow bed surface area

Simplest ratio 1:1, easiest to start with but if you go for 2:1 then realise you will need a sump and possibly a second pump.

Tank requirements  Water proof  Strong – water 1000ml = 1kg, 1000ml of clay = 450g, along with plant = heavy and need to be strong – hydroponic tanks are lighter due lower depth of grave  Toxicity Non toxic – food safe. Recycled plastic what was its origin – container and the plastic  Inert – does not react or decompose- not metal or uncoated concrete.

Grow bed considerations.

 Grow bed area will dictate the size of the whole system / pop of fish etc. Therefore you need enough fish to support the plants.  Consider 1:1 ration of fish tank to grow bed vols

Aquaponic grow bed zones:  Zone 1 first 2” – fry zone stops collar rot, sunlight pentration,  Zone 2 15 -20cm bio filtration with water and O2 in balance  Zone 3 Bottom 5cm where solid collect

Bed depth 12” the norm and should not need cleaned out.

Fish Tanks

Key considerations:  Tank food grade material – no toxicity  Min 190 l  30cm deep  Larger tanks small fluctuations in pH and temp  Shape – better flow dynamics and solids collect etc.  Pump can keep water partially distributed in the tank  Fish tank have a good surface area (flatter in shape)  Position carefully for weight and insulation  Disturbance – shade / light  Tank cover

Metal and plastic tanks – Pros: Plastic widely avail, strong, non toxic, flexibility Cons: expense, carbon foot print

210l drums Pros: recycle, available, cheap, Cons: complex framing, previous use? Aesthetics, limited to one size

Intermediate bulk containers (IBC) 1000L & 1250L

Can cut the IBC in half fish on the bottom and plants on the top – grow bed 35cm depth. May need to consider reducing stocking density as will not achieve a 1:1 ratio. Alternatively can use several IBCs to the fish tank.

Pros: inexpensive, come with frame,

6 Cons: not UV stable, previous use? Cutting half challenge, only half the vol of media bed to fish tank vol. water tightness of the top?

Flexible pond liner

Pros: flexibility, easy to install / transport, strong, insulated in the ground Cons: if using a frame – extra work and puncture risk,

Aquariums Pros: good for seeing fish, having indoors, range of set ups available Cons: for indoor use only, subject to temp fluctuations,

Bath tubs Pros: Recycle, Cons: limited size – 150l

Manufactured kits

Evaluating systems

 Manufacturer experience – do they have it?  Manufacturer reputation – check out – other users, google, Utube,  Kit quality  Kit content and instructions etc

Pros: save in time, heart ache as the manufacturer has already done this for you therefore concentrate on what you want from aquaponics, attractive Cons: cost, lack of expansion potential?

Swimming pools

Issue of volume and how to incorporate this into working principles of respective vols etc. Also toxicity issues. Example of only using the deep section of the pool and the rest for other growing acitivities.

Vertical growing Plastic bottles Use simple plastic bottles upside down hung above an aquarium

PVC towers: Use 110 pipe – cut pipe half way, heat with air gun & push in.

Chapter 8

Plumbing

Pump Considerations: flow rate, head pressure, pipe work, - quality of pump. Aim for tank to t/o once per hour. Is it going to be continuous or timed – this will influence flow rates required. Discuss issue to do with working head etc.

The Pipes PVC or Chlorinated PVC – widely available, food grade, option to glue or screw. Different systems of joining, cutting, measuring – to glue or not to glue? Consider issues of clogging, access to pipe to clean etc.

Downside use of plastisers – best to reduce, reuse, recycle

Tank connectors – only real option

7 Timers – can be used to switch on pumps etc. Aquaponic systems flood drain much more frequently than hydro ponic due to the need of the fish to have regularly filtered water.

2 configurations for pumping:  Pump through pump and fill up until about to overflow and switch off Pros: simple, less chance of clogging Cons: solids are entering where water is entering therefore less opportunity to process waste etc.

 Pump to surface of grow bed, trickle through – with the exit smaller than the inlet Pros: distribute water where you choose, Cons: solid waste draining through could lead to clogging. Problem of switching pump on and off

Tanks need to have an overflow / stand pipe to stop flooding of beds.

Auto siphon – no timer needed.

Water rises in the tank, reaches its maximum level- spills over a pipe creating a low pressure area within the siphon and triggers the water movement. No moving parts to no energy and long work life. Can add an aeration bar.

102 & n103 construction of Auto siphon

Need a valve to control water entry to ensure the siphon will function. If siphon does not work try:  More powerful pump  Decrease the diameter of stand pipe to restrict flow  Add horizontal pipe to outlet which will create back pressure

Horizontal pipe and perforated under sides to pipe to allow leakage to growing beds

Sequential valves Aeration pipe spray bar Backup / contingency arrangements for pump breakdown etc.

Chapter 9 Media

Soil is a ‘black box’. In Aquaponics the soil is deconstructed into:

 Structural: a structure for roots of plants and an environment for bacteria. Greater the surface area the greater the potential population of bacterial – Specific Surface Area SSA – M2/M3  Biofilter for solid waste: aerobic and hetertrophic bacteria and worms break down solids  Composting worm home  Air and water exchange: good porosity and continually irrigated  Temperature moderation

Media – essentials:  Not affect pH e.g. limestone?  Not breakdown/decompose  Correct size 12 – 18mm

Media – non essentials  Porosity and light in weight  Easy to handle light and no sharp edges

Good gravel: granite, other which are pH neutral etc.

8 Carry out a trial – in a bucket etc for a week

Washing media

Expanded Expanded River stone Crushed Synthetic Shale clay stone Weight 75% of stone 50% of stone Heavy Heavy Lightest Environmental Mined Mined Mined / Mined Made from extracted petroleum Origin US Germany/ UK UK China? China pH neutral Yes Yes ? ? Yes Easy on the Yes Yes Normally No Yes hands Expense 1- 3 4 2 1 5 low, 5 - high

Chapter 10 Water

Mains

Normally pH neutral due to pipe corrosion.

Contains Chlorine – leave to stand for 24 hours, aerate will accelerate the process – pH may change. Up to 10% not a problem to add. Require more have storage so you can have access quickly. Alternative use a dechlorinator. Chloramine used?

Alternatives – rainwater or ground water Get it checked – pH, General hardness

Temperature Choose fish which match the temperature regime of the locality because:  Be aware of the tolerable temp range and the optimal temp range for spp  Minimise heating, insulation, costs and effort  If power failure fish will have a better chance to survive if normal temperature = their normal temp range.

The over lap of acceptable area for fish and plants/bacteria is much greater for warm water spp of fish than cold. Therefore need to consider heating water either passively or by additional heat.

Attract / retain heat

 Have a black tank  Insulate tank – walls and floor  Double skin the greenhouse or building?

Adding heat

Less than 750l use an aquarium heater 200w heater for a 200l tank or have several heater better of one thermostat.

DO Affected by:  Temp  Altitude  Salinity  Biological activity in the water – microbes  Amount of fish in the tank

9  Moving and stagnant water  Different fish have different tolerances to DO levels

Rule of thumb 6ppm absolute minimum 3ppm

Measurement without the use of a DO meter:  Maximise DO levels – spray water where you can, use water going through other systems – e.g. gutters  Observe fish – do they feed well?  Use an aerator pH

Optimal pH for:  Fish – 6.5- 8.0  Plants -5.0 – 7.0  Bacteria and worms – 6.0 - 8.0

After established, pH can drop due to nitrification of ammonia to nitrate and can account to 90% drop in the pH. Adjust if pH drop below 6.4. Raise by using alternatively hydrated lime and potassium hydroxide. Natural forms of calcium carbonate such as egg shells can take a long time to dissolve. pH rising due to:  media not inert?  Adding hard water to the system?  Anaerobic spot in grow bed

Adjust by pH Down solution, nitric or phosphoric acid , other strong acid such hydrochloric, sulphuric – last resort

Section 4 Software –

Chapter 11 Fish

The heart of the system – they move and respond and provide the food for the plants. They do not ask for much. More than any other culture system they demonstrate clearly how things actually are interdependent. A unique educational tool.

Stocking 1kg = 40 – 80l for media based aquaponic system 3kg = 30l of water 1 fish = 20l of water as a rule of thumb in a backyard aquaponics system

Species  Tilapia – easy, warm water, tolerant of DO levels, reaches 700g 9-12 months, tastes good.  Catfish as above  Gold / Kio fish for not eating  Perch  Carp  Trout  Grass carp?  Cray fish

10 Temperature

80% of energy for a mammal is used in maintaining an optimal temperature where fish use none. Fish have a FCR of 1.5 compared to cattle which is 7.

Fish are also supported by the water column

However fish do not have control over operating at their optimal temp level therefore it is the farmer who has to manage this to maximise production.

Choosing the correct spp best for your situation bearing in mind the aim to achieve optimal performance at all times. Option to use warm water spp in summer and cold water spp in the winter is difficult because it can take up to a year for the fish to reach harvest size. Options for using half size fish or rearing different spp at same time.

Eating habits

 Carnivores need high protein feed which normally requires buying feed or growing grubs. ]  Carnivores there is a need to keep them at a similar size and same spp  Omnivores can mix different spp and sizes and have the option of eating a range of feed some of which can be reared at home.

Tilapia and breeding in tanks – strategies for controlling number p 145 -146.

Feeding fish

Observation is the best, problem using automatic feeders etc. ~Feeding to table.

Commercial feed – pros and cons Other feeds, worms, soldier flies, kitchen scraps – bland tasting, non flowering even fruit.

Chapter 12 Plants

Water – key differences with agriculture. The story of how agriculture has changed from natural systems to insuring there is water available for plants (irrigation, humus etc). However as water is still ‘separate’, need to deliver through irrigation – requiring effort and can lead to peaks and trough in water supply ie not always stable continuous environment.

With aquaponics – stable and continuous plenty water and oxygen. Less roots need to grow and therefore more goes into fruiting and growth above ground. Use far less water unlike agriculture

Food for plants

Nutrient requirements

Fundamental nutrients Macro nutrients Micronutrients Carbon Calcium Boron Hydrogen Nitrogen Copper Oxygen Magnesium Iron Phosphorous Manganese Sulphur Molybdenum Zinc Aluminium

In soil – organic matter decomposes and latterly goes through mineralisation phase rendering the nutrients available to plants.

11 Hydroponics bypasses this phase and adds the mineralised solution directly to the plants. Nutrient levels change either through depletion or higher concentrations etc – can dilute but eventually the whole solution has to be replaced.

Aquaponics – as the waste is soluble and fish are cold blooded? The solution can be readily mineralised in the grow beds. Some nitrogen can be directly absorbed by the plant even without bacteria.

There should be no need to dump as long as: Correct stocking densities, grow bed to tank ratios, pH levels etc. Well established system (up to 6months to develop) i.e. Nitrosomonas and Nitrospria – ammonia and nitrite conversion. Hetertrophic bacteria established to break up solid fish waste. Once established an aquaponics system will be more productive than hydroponic system. Start off with lettuce etc which are less demanding on nutrients and then introduce tomatoes etc later which are more nutrient hungry.

Air

Oxygen is carried in the water and following the ebbing of the media bed – plants need the oxygen as well as the fish.

Structure

Plants without roofs are floppy i.e. see at the side of a pond – with media or soil it is supported and wraps itself around it.

Temperature Warm season plants can’t survive below 13oC, and not thrive until 18oC. Tomatoes prefer a root temp of 24oC.

How to start plants in and for aquaponics

Seeds – issues concerning biodiversity and the loss of crop diversity of 75% from 1900 to 2000.

Seeds can be broadcast directly on media: luttuces, radishes and carrots

Paper towel – seeds which germinate very quickly but are larger than lettuce – melon, peas, beans, cucumbers. Seal in bag and once root 25mm long transfer to grow be making sure the root is within the flood zone.

Seed trays using range of seeding materials

Starter plugs

Pros: inert, pH stable, pleasant to work with (instead of rock wool), bio degradable, work well Cons: expensive relatively, fungal knats?

Cuttings……… pH and nutrient supplement p 165 scan chart showing nutrient availabilities and pH. If have an iron deficiency look at stocking and feed being used. Need to keep records etc – good for courses demo.

Integrated Pest Management  Stage 1 Either tolerate or remove offending platnt  Stage 2 Monitor and identify pests  Stage 3 Prevention – stop them entering  Stage 4 Control starting with the less risky – be aware of the potential impact on the fish and plants – options:

12 Feed to fish  Knock pests of with spray etc.

Use of live predators / parasites  Ladybird – eat aphids and will lay eggs near to aphids, within a week hatch and within a month pupate and week later hatch. Eat also mites, soft bodied pests.  Lacewings – the larvae which predate on aphidsa others – eating 200 pest per week/ larvae. Pupate and hatch in 5 days. Normally 5 -6 generations / season  Parasitoids – wasps, flies, rove beetles – victum specific. Widely used is Encarsia formosa for controlling fruit fly. Control is slower but life cycle is quicker compared to predator spp.  Beneficial planting to attract predator insects: fennel, coriander , dill

Spraying with organic solutions

 Murry Hullam few table spoonfuls of molasses with a litre of water and a teaspoon of dish soap. Spray on plant (not fish tank) – this make the crop less attractive to eat  Insecticidal soap – work by wash protective coat of the insect and then break cell membranes leading to cell death. E.g garlic, onion, teaspoon of cayenne pepper make to paste, add to 1 litre of water, stand for an hour, strain and add tablespoon of liquid soap. Use within a week.  Neem  Bought organic insecticides.

Chapter 13 Bacteria and worms

Aquaponics is about farming bacteria. Sustainable food production focuses on the connection the inputs and the results. Manure and sunlight are connected by grass to the meat or milk. The fuel in aquaponics is the fish, while the engine is the bacteria. It needs to be nurtured and cared for.

Nitrifying bacteria Nitrosomonas and nitrosprira - some points of interest:  They are aerobic  Need a surface to grow on  Need a moist environment  Doubling time 15 – 20 hours while heterotrophic will produce 35 trillion

Chemical reactions:  Nitrosomaonas NH4+ + 1.5O2 > NO2- + 2H2O + 84 kcal/ mole of ammonia  Nitrospira NO2- + .5O2> NJO3 + 17.8kcal/mole of nitrite  Overall NH4+ + 2O2> NO3- + 2H+ H2O + energy

Caring for nitrifying bacteria  Rapid changes e.g. temp, stocking will impact on the effectiveness of the bacteria to do the job.  Optimal temps: 25 – 30oC  At 18oC growth rate is decreased by 50%  8 -10oC growth rate is decreased by 75%  Stops at 4oC  Killed off at 0oC or 49oC

Oxygen supply is crucial and dead areas become uninhabited with nitrifying bacteria and toxic level of ammonia accumulate. With DO of below 2ppm, dissimilation by hetertrophic bacteria can convert NO3 back to ammonia and nitrites!

Optimal pH 7.8 – 8.0 range 6.0 -8.5 – Nitrosomonas Optimal pH 7.3- 7.5 range

13 All nitrification stops below pH 6.

Worms

Can digest the solids in the media converting to worm tea.  Evidence suggests that worm tea can:  Suppress plant disease Pythuim Rhizoctonia  Suppress parasitic nematodes  Suppress plant insect pests – spider mites, aphids

Dosage: 1 kg of worms to 1m3 of media

Section 5 Integrated system

Chapter 14 Cycling

Cycling with fish

Adjusting pH

Start of gradually and build up. Consider using sacrificial fish. Feed once a day. Ammonia which is toxic varies with pH – in terms of a dynamic equilibrium. It is more toxic at higher pH’s and temp.

Aim to keep pH at 6.8 due to ammonia toxicity. Once cycling the idea set pH is 6.8-7.0.

Nitrite >10ppm - water exchange. Also add salt @ 1kg / 1000l. Stop feeding fish & aerate. Used as the chloride ions bind with the nitrites and reduce toxicity.

Fishless cycling.

Pros: Less stress You can elevate NH4 much higher than is safe for fish leading to shorter time to cycle – 10 days Can be more precise in controlling levels of ammonia and the need to add more or less depending on the results of the water tests.

What to use: 100% ammonia or ammonium hydroxide – in its pure form. May be difficult to source.

Ammonium Chloride (crystallized ammonia) Urine – There is a need to bottle for a few weeks for it to convert from urine to ammonia and there is a danger of spiking during cycling/.

Method:  Add a little until concentration of 2-4ppm – record the amount added  Add this amount daily until nitrite appears (at least 0.5ppm) If ammonia reaches 6ppm stop adding until the levels return to 2 – 4ppm  Once nitrites appear cut back on daily ammonia doses by 50%. If nitrite rises to 5ppm, stop adding ammonia until it drops to 2ppm.  Once nitrates appear (5-10ppm) and nitrites and ammonia dropped to zero you can add fish – stop adding ammonia.

Adding plants

Plants can be added straight away as they take up nitrogen immediately, though adding seaweed product – Maxicrop. It is a growth stimulant especially for roots. Dosage 1l per 1000l

14 Alternatively

Add liquid seaweed to the system Add plants Wait for two weeks Add fish – at lower stocking density

Other option to seed the system from another source e.g. another system

Managing water temperature and cycling development

 25 – 30oC Optima l  18oC – 50% longer  8-10oC – 75% longer

Maintenance

Daily:  Feed fish  Check water temp  Check auto siphon and pipe work etc.

Weekly  Check pH if dropping buffer up. If rising check if anything is being added or is there a dead zone in the grow bed.  Check ammonia levels should be less than 0.5ppm also for nitrites  Top up water if needed  Check for insects  Stir up gunk on the bottom of the tank

Monthly  Clean out the pump and pipes  Nitrate tested – if > 150ppm either harvest, plant more or add another bed

15