Backyard Aquaponics

How to reduce nitrate in AP ?
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Author:  Nit007 [ Dec 14th, '18, 02:07 ]
Post subject:  How to reduce nitrate in AP ?

Currently nitrate is 160 ppm despite max plants in the system.

Author:  dlf_perth [ Dec 14th, '18, 07:24 ]
Post subject:  Re: How to reduce nitrate in AP ?

no magic solution....

#1 more plants
#2 more grow bed
#3 do water changes
#4 stop/reduce feeding fish
#5 reduce number of fish

you say you already have max plants so you probably need more grow beds...

#3 is a short term answer, but you wont want to keep doing it.

nitrates are not too bad, but you want to get them down.

Author:  Terra [ Dec 14th, '18, 09:12 ]
Post subject:  Re: How to reduce nitrate in AP ?

This problem pops up all the time

System runs ok until fish grow

Too much of one nutrient will trigger deficiency in others so eventually the situation will need to be resolved

Short version is system is not "balanced" , there is too much nutrient produced for the plants too handle at this time

Solution is as Darren highlighted

This is one of the skills required in aquaponics , the planning ahead for managing plant / fish , do less sooner , so we are providing a solution instead of reacting to a problem

My 3000L 5 growbed system system is reasonably stable , however with only 12 "plate size" murray cod and only 50grams of feed a day my nitrate is sitting around 80 ppm which is about twice what I would like .

I have packed in 30 corn plants to help with this , on top of my other plantings

I often suggest regular small water changes however this reduces your general nutrient base as well , so again as Darren highlighted short term only .

Can you build something off the side that you can bring online as required and fill with hungry plants , perhaps a floating raft , or a tank with water plants .

I have one growbed stuffed full of silver beet I don't eat much myself I use it as greens for my chickens , point being find something that will do the job .

Nitrogen is loved by leafy greens eg grasses , celery lettuce

Potassium is loved by fruiting plants , eg tomatoes

Phosphorous is loved by root crops eg beetroot

We love photos


Author:  Mr Damage [ Dec 14th, '18, 12:06 ]
Post subject:  Re: How to reduce nitrate in AP ?

If all you want to do is reduce Nitrate, then cut a blue barrel in half, plumb it into the water flow in your system somewhere in such a way that it's nearly full of water and has a slow flow through it. Have it sitting in full sun if possible, algae will very quickly grow in it and your Nitrates should start falling. Make a cover for it, so that you can stop the algae growth whenever it suits.

You can also use the same tank as a dosing tank, for adding pH raising/buffering agents etc into the system, so it's a more gradual release into the system and doesn't build up grit on the floor of your FT, ST, or GB.

You could also achieve the same effect by just exposing part of your FT or ST to sunlight, but I'd be hesitant to promote algae growth in either.

Algae can very effectively reduce Nitrate levels. Once, while fishless cycling a new system, the Nitrates had reached 80ppm. I had a small patch of algae start growing in a corner of the IBC FT that was exposed to sunlight. That dinner plate sized patch of algae reduced the Nitrate from 80pp to 20ppm in just 3 days, bearing in mind there was no more Ammonia going into the system, so no new Nitrate being produced.

Over the years I've found that in many systems the ratio between Nitrate and the mineral nutrients tends to blow out with time and they could do with having the Nitrates reduced without reducing the other nutrients, as would occur with water changes.

Author:  Mr Damage [ Dec 14th, '18, 14:33 ]
Post subject:  Re: How to reduce nitrate in AP ?

Also, something else to keep in mind, it's very common to see people posting on forums etc, that they have a Nitrate level of 160ppm, when in actual fact it is much higher. Because it's the highest reading on the chart, as well as the fact it's a very dark colour, once your results get above 160ppm it's very difficult to discern the correct level, so it can actually be much higher, which isn't good for your plants or your fish. Try watering down your sample by 50% and see what result you get.

Author:  dlf_perth [ Dec 16th, '18, 20:34 ]
Post subject:  Re: How to reduce nitrate in AP ?

>> Algae can very effectively reduce Nitrate levels

Duckweed is another, potentially effective method, and can be fed to fish.
But need the surface area for it, so weighs up against another bed of plants or a few dutch buckets

>> they could do with having the Nitrates reduced without reducing the other nutrients, as would occur with water changes.

if water changes are going to other parts of the garden/wicking beds etc then there is no real issue, ultimately there is still benefit from the nutrient enriched water in some part of the broader system. Nutrient loss is not really likely o be a major factor in most small BYAP systems - and can always just add some seasol/lime or whatever required for pretty low cost if required.

The bigger issue is don't want to be always doing water changes - indicates an out of balance system.

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