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I have a 275 gal IBC tote for my fish tank, and two, 3' x 6' x 1' grow beds. Because of distance from the sump tank, one is on a flood and drain pump system, 15 minutes every hour, and one grow bed uses the bell siphon.

I started my system in late April, and it took about a month until ammonia levels dropped to zero and nitrite levels dropped to zero and nitrate levels were about 40 ppm.

I added 25 Tilapia, to about 10 mosquito fish that I had put in, about mid June and the first two months everything was great.

In late august the plants ( herbs, strawberries in one grow bed), peppers and squash in the other. Began to look a little rough. The weather here in so cal has been incredibly hot for nearly a month.

Recently, the past three weeks, the ph is up to 7.4, ammonia levels between 0.25 and 0.50 ppm, and nitrite levels are at 1 ppm. The nitrate level is over 80 as well.

The fish are getting really big... (well, from where I started), but I am really concerned about these levels and I had a dead fish (one of the small ones- not a Tilapia) the other day. I got it out of the tank immediately.

I did a partial water change.

I've added pH down. Not clear how much to add, between my sump tank and my fish tank, the total volume of water is probably 500 to 550 gal. Water temperature is 82 to 84.
How do I lower the nitrite levels safely?

How much ph down do I add to achieve the pH I'm looking for (7.0)?

I noticed the problem after I went away on vacation, and had my kids taking care of it. I'm thinking the fish may have been over fed, but that begs the question, really how much is appropriate to feed them?

Currently giving 2 to 3 teaspoons twice a day.

Food purchased from Sylvia.

Thanks for any help you can give


Roasting in Southern California

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Interesting Problem.

See if I can spark so me more knowledgeble conversation.

Ammonia = Fish waste or over feeding

Nitrite = Bacteria 1 conversion

Nitrate = Bacteria 2 and plant consumption.


Equation suggests your not using your nitrates. More Plants?? I have water hyance and duck seed in abundance in the wild where I am so I can add and subtract this natural filter as I see fit.

"Plants are looking a little rough" define rough. Heat Stress, Over Growth.

"Over fed" if all the food is not gone in 15 minutes take the remainder out reduce later feedings until balanced. (Feed to eat to time)

"Changed out half the water" Wooooo there slow down 15 changes to one problem. Ok what fixed it for knowledge next time?

7.4 PH and you added PH down but did not know how much. Tilapia can take much larger PH swings than that. Just not all at once. Be gentle.



Nice hair.






Everything suggests that your system, still relatively new.... is on the edge of your feed rates... (the kids might have over-fed a bit while you were away)....

But I think your results, and plant observations give the clue as to what is the possible cause... and ultimately the response...


Everything suggests that your nitrification is working... although it might be at a limit of the filtration you have... and the nitrates certainly suggest that you could perhaps add another grow bed, and plant more plants...

But it could be just that the plants are "struggling" to take up the nitrates...

You note that the weather has been very hot.... well as water warms... it holds less oxygen.... and fish and plants need more oxygen as they grow...

So to, do the nitrifying bacteria... remember that the conversions of ammonia... to nitrate.... are both oxidation processes....


I would suggest that you..  need to add additional aeration to your system... an external air pump, preferably a battery backup arrangement...


And I'd also suggest... that you should consider altering the timing period for the bed concerned during hot weather...  i.e 15/15, or 30/30.... (are you running two pumps??)


Your results suggest that nitrification is proceeding... and that your pH will undoubtably trend downward shortly...


I wouldn't be adjusting pH... just let it fall naturally....


If your top up water.. and I'm sure you're topping up.... has a high pH... then you could treat it with Hydrochloric acid... don't use pH Down.... before adding it to the system...


Once your pH has dropped naturally... just add untreated top up water....


Don't water change..... just add aeration... and/or increase pumping frequency... and salt to 1ppt to mitigate against the nitrites....



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