Aquaponic Gardening

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Hello, Aquapons, and thanks for all your help so far.  Now I find myself with a pressing problem – we just got fish, at long last (hooray!), but our system water isn't ready for them and I'm not sure why.


Here's the situation.  Our water quality tests look like this:


Ammonia:            0.2 ppm

Nitrite:                  7 ppm

Nitrate:                10 ppm (even accounting for nitrite interference in the tests)

pH:                      7.3

Temp:                  82 degrees F

DO:                     6.6 ppm

Chlorine:              0.2 ppm (this is new)


The nitrites are what I’m worried about.  Above 5 ppm is toxic – yes? – and we have tilapia fingerlings that need somewhere to go.  Right now there are 1800 of them in about 2 cubic meters of aerated water, which sustained them overnight, but the ammonia in there is already up to 3 ppm and they're starting to look stressed.  (Long story why we didn't put off getting them when our water is imbalanced…) We can (and will) do a partial water exchange with captured rainwater, but our running water is off and likely to stay that way, and so that'll only tide us over for a day or so.  I need to figure out why our nitrites are so high and what we can do about it.


Nitrites, Nitrates, and Ammonia, respectively.


Some background on what's been up in the system: 

  • About a week ago, a whole bunch of bullfrogs laid their eggs in a new, marvelous water source, and we have HUNDREDS of tadpoles in both our troughs and our tank.  Our DO levels have dropped about 1 ppm since then, and we have trace ammonia even without fish and with no other source.  I see them nibbling on filters and raft bottoms - could they be eating all our bacteria? (A side question – will they eat our plant roots?)
  • We've had to add water to the system several times in the past few weeks, trucked in – each time, I tested the water for chlorine before it was added, and found 0.0 ppm. (And, every time except one, we let the water offgas for four days anyway before circulating it.)  So I don't know where the reading of chlorine is coming from.
  • We're using new test strips now – the other test strips (made for pools) show 0.0 ppm chlorine and pH of 6.8. (Does anyone know an independent way to check which is right?) The results from new test strips match pretty well with the chemical tests on ammonia, nitrite, and nitrate.
  • About a week ago, we brought our second trough online, bringing our raft area up to about 1000 square feet.  The system is currently about 80% full.
  • We just put greenhouse cover and pest screen on hoop houses over both troughs.
  • We've been spraying the plants with neem to control pests.  The trees grow everywhere here, so we've been blending the fresh leaves with pure water and straining the mixture to get a rich juice (with a small fraction of oil).  Our agronomist, who studied Crop Sciences at university here in Ghana, is very pleased with it. 
  • We added 1/2 liter of seaweed extract to the system two weeks ago, and the other half early last week.  We saw a significant spike in growth rates after that.


The system has been running on fishless sources of ammonia (better since my last post on that, and thank you for directing me to Vlad) for about a month.  I inoculated it with ProLine immediately, and we were showing nitrates in 6 days.  We haven't stopped showing nitrates since then, so I don't think this can be a standard startup nitrite spike.  But now, our nitrites have been around 6-7 ppm for over four days with no discernible change.  Any ideas what this is?  Any ideas for how I can drop our nitrites in the next 24 hours so we can put our fish in?


Any and all help is much appreciated, from the fishies and me!


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You said your DO levels dropped to 1 ppm!!!!!

That is probably what is messing with things.  The bacteria need dissolved oxygen to work so if something (like tadpoles or something else) has cause your biological oxygen demand to increase or something else has caused your aeration to loose efficiency, then that could well be the cause of water quality issues.

Use salt dissolved in the water to help mitigate nitrite toxicity and add as much extra aeration as you possibly can to help get the bacteria back up and running.  Tilapia can handle quite a lot of salt (plain old solar salt for pools or water softeners is fine.)  You need between 1-3 ppt of salt which will mean a lot of salt for a big raft system since you have to figure the entire water volume.  However, if you will be doing water changes, wait till after the water change before adding salt and then hopefully don't do any more water changes or it will be nearly impossible to know how much salt you have in the system unless you have the tools to measure salt levels.

If you have any anaerobic or anoxic areas in your system that could account for high nitrites.  Check your aerators and make sure everything is flowing properly.  (make sure your pump intakes are not clogged with tadpoles and that the airstones are putting out the right amount of air.)

Sorry!  No, our DO levels dropped BY 1 ppm.  They were at 7.7 two weeks ago, but since the tadpoles it's come down to 6.6.  (Caveat - this is measured where the water returns to the pool, which is our current point of maximum aeration.)

I'll still scout around for anoxic areas - thanks for that tip, I didn't know those could cause excess nitrites!

And - salt, aye. 


There is a process called de-nitrification that uses anoxic conditions and can actually convert nitrates back into nitrite (after which you would want to have a degassing tank or some other means to really blow a heck of a lot of air through the water to allow the nitrogen to escape into the atmosphere rather than being in your system as elevated concentrations of nitrite, those same anoxice or anaerobic conditions can also cause other bad gasses in the water like hydrogen sulfide so in aquaponics we usually try to avoid the anoxic or anaerobic places.)

Here is a link with some numbers to help those not on the metric system to figure out how much salt to use.  Keep in mind that I'm in the USA so I use US gallons in my figuring.

Because of de-nitrification Nitrite remains constant in my system while Nitrate is very low. My solution is: 

1: Clean my filter medias that get clogged with excess amount of fish-poo (But not smell bad). Ensure that there is no anoxic condition in the filter systerms.

2. Add more air stones to Bio-fitlers (If you have them in your filtration) to improve the beneficial bacteria's performance.  


Chandara, I like the pretty blue pipes you guys have there.

Thanks TCLynx ! Here blue pipes are cheaper than white pipes that's why they are the first choice. To me I prefer white pipes. 
TCLynx said:

Chandara, I like the pretty blue pipes you guys have there.

Chandara, you could add a solids separator before you filter to reduce fish poo going into it. 

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