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I have a 1400 gal FT, 2 80 ft troughs( about 1800 gal each). I was fishless cycling and at 2ppm ammonia and nitrites were just starting to show up when I added 200 3"-5" catfish on 11-1. PH was about 6.8. Within a week nitrites were 5+, ammonia .25 ppm, PH 6.2 - 6.4, nitrates 10 -15- ppm, water temp 65.5 - 66.5. I have been removong 1/2 my rafts daily for a week now and all levels remain constant. 6 fish have died in the last 3 days. I tried checking with a test strip also for 3 days now and it says 1 ppm nitrites and .5 nitrates, but I tend to believe the test kit more. I thought the nitrites might be coming down but it is so hard to judge the color chart at the higher levels of nitrites. If I start doing water changes I will use well water which is 58 degrees and has a ph of 7.2 but I am afraid that might stress the fish. Can someone please give me some suggestions.

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You might salt your systems water to 1ppt to help mitigate the nitrite toxicity that your fish are experiencing. Traditionally this has been done with NaCl, but a number of us have been salting with say about half NaCl, half KCl for the added benefit (plants) of potassium that the potassium chloride brings. Though it's the chloride ion that inhibits nitrite poisoning in fish, so either way...Just make sure whatever salt you use contains no iodine or anti-caking agents. Most big box stores carry both types of salts. NaCl is sometimes called "pool sat" or "solar salt", and KCl seems to be sold as a "water softener". Home Depot should have both. 1ppt is one part per thousand. TC has a helpful blog on how to go about figuring out weights and measures

Hi Pete,

The fish are already stressed, so its not much of a risk in doing a 50% water replacement(immediately). Be sure not to feed the fish at all until all the Nitrites are gone from the system water.

One thing I did in conjunction to what Vlad said was I increased my rate of flow into the grow bed for 24 hours after salting.  Within 36 hours the nitrites dropped to close to 0.  I also did a 25% water change.  Those recommendations came to me from Vlad and TCLynx when I was having a problem with Nitrites.  All remaining fish survived and healed.

Thanks for the responses so far.

Now that I've salted  to 1ppt what can I do to reduce the nitrites? I have been removing at least 1/2 my rafts every day for about 10 days now and my nitrites are still about 5 ppm.

You can dilute the nitrites by a partial water change if they don't start coming down. Adding fish as you say "just when nitrites were starting to show up" probably wasn't the best timing, but what's done is done. Salting will help, a partial water change may help dilute some nitrites...Other than that, I'm not sure what else you can do...Increasing water flow certainly would not hurt.

Question: do you have any sort of "dedicated" bio-filter, or just the DWC troughs? 

I do have a 50 gal tub with 1/2-3/4 gravel that my water filters through between the ft and troughs. I would have liked to wait longer before fish but that was when the hatchery was making their delivery.

Just wondering since you're taking off half your rafts (to kill off some N.sonomas with UV rays, I presume)...I'm guessing though, that much of your NH4 oxidation (to nitrites) is taking place in that 50 gallon tub. Hopefully the worst of the NO2 spike is over.  If not (and I know it's no small thing to dump and exchange that much water) you might want to start preparing some water to exchange with (25% or so). You can always pH adjust with HCl before you add it to the system. Not to make you feel any worse but, catfish it seems are among the most sensitive to nitrites, but if you've lost (and hopefully those will be the only ones) only six...that's not that bad at all. 

Here's some good info on nitrite/chlorides in relation to different fish species (catfish included)...It should help you understand what it is exactly that you've done by nitrite poisoning exactly it is mitigated etc...If nothing else it may help calm you a bit

Thanks for the info. It has been 48 hours since I salted and increased water flow. My nitrites at last check were between .25 and .5. Ammonia was up from .25 to .5 (I believe that is due to the fish that died). My nitrates are 10-15. I am hoping that by tomorrow morning I should have a nitrite reading of 0. After i salted I stopped removing 1/2 my rafts. A week of sunlight did nothing to reduce nitrites, in fact, I think removing rafts only reduced surface area for the bacteria to grow and slowed down the whole cycling process. Thanks for all the advise. I 'll update in a day or two.

Very cool! I bet you're glad that, that's over...

My ammonia has been down to .25 ppm for a week now and nitrites came down to .5 for 1 day and has been .25 for 3 days now. will both levels ever come down to 0 or will they stay at about .25?

Check the numbers on the bottom of your reagent kits...Last year I seem to remember trying to get some of us to document what happens when the reagents are past their date of expiration. if I recall correctly it seems that for some reason they wont record a reading below 0.25 when they are old (past the expiration date). Don't quote me on this yet, since it's been a while, but I'm pretty sure that, that was the cause (old reagents) of 'the ol' no readings under 0.25 bit...

It's a weird piece of info/detail, I know...but check it out before you go batty trying to get a 0 reading.

The "LOT" number at the top of API test kit bottles are the date of manufacture. The API test kits typically expire 3 to 4 years after the date of manufacture depending on the type of test kit. These were the expiration periods that I found from API:

Ammonia Test Solution # 1 - 3 Years
Ammonia Test Solution # 2 - 3 Years
High Range pH Indicator Solution - 3 Years
Nitrate Test Solution # 1 - 3 Years
Nitrate Test Solution # 2 - 3 years
GH Test Solution - 3 Years
Calcium Test Solution #1 - 3 Years
Calcium Test Solution #2 - 3 Years
Phosphate Test Solution #1 - 3 Years
Phosphate Test Solution #2 - 3 Years
Copper Test Solution - 3 Years
KH Test Solution - 4 Years
Nitrite Test Solution - 4 Years

I will look into the dates. When I first put the drops in the color matches with the zero reading but within 1 min it changes. thanks for the quick reply.

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