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I've been reading up on nitrite tolerance of fish. As with many things, the answers are complex and dependent on many things. Here's my situation:

Added 12 healthy 4-6inch Bluegill to my fully fishless-cycled 60 gal tank (40 gal heavily planted media growbed). Prior to adding fish, my system would process 2-4ppm of Ammonia straight through to Nitrate in 24 hours (in my case, a quarter teaspoon of powdered ammonia gave 2-4ppm).

Once the fish entered, ammonia spiked briefly to 2ppm, and has been consistently zero for days now. Nitrite jumped to 1ppm and seems stuck there. So it would seem that I am processing ammonia faster than nitrite, so I have a bit of "nitrite backup" perhaps. Note that I have not fed fish since they were added 5 days ago, so I'm a bit confused as to why nitrites are stuck at 1ppm.

My concern is the fish seem listless and are not eating at all (5 days now). My understanding is that days of nitrite exposure are bad - at any level. My water is clean, warm (72 degF), I clean up any uneaten food, bottom of tank is clean. Ph is good at about 7.0. Water is heavily aerated, so I believe DO levels are high. Growbed is super-healthy and heavily planted.

So, would a nitrite level of 1ppm keep fish from eating? Do I need to be concerned about the 1ppm nitrite - enough to start doing water changing?

Or maybe my fish are just tired of seeing me hovering over them :)

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If the fish came from the wild, they aren't accustomed to being in a tank and eating commercial food.  In any case, I've read that fish generally don't feed for a few days after being moved.  I thought I was cycled but wasn't and stocked bluegill and catfish.  I had nitrite for a while, much higher than yours - most of the catfish died and most of the bluegill lived.  They feed well at this point when the water is around 60F or so, less when cooler.  My system is outside so the water temp varies by day and time of day.  My nitrite has been at 0 for a couple of weeks or more now.  I don't believe 1ppm nitrite will hurt your fish but I also wonder why it is 1 ppm if you are cycled and the fish aren't feeding. 

They are stressed from the nitrite level, some fish act sluggish and will not eat when exposed to those levels.  Some fish die in a few hours at that level.  The whole bit about not feeding after moving is not really that true.  I move fish all the time at work and feed them moments after.  Heck I fed fish moments after un-bagging them from Asia one time and they were bagged for 3 days.

It has been shown that centrarchids can handle higher levels of nitrite, but you are correct below .5 is way better. If you are on well or spring water, check it.  We have nitrite and nitrates in our spring water from time to time.

Your situation is weird,did you acclimate the fish before the addition? 

Are they wild? 

Do you have a cover over the tank?

The fish were moved from 1000gal greenhouse tank to indoor 60 gal tank. Temperature and pH was matched already, so no acclimation was done. Tank is half covered, so has privacy in back. They do scoot to back whenever I enter room, so they don't like my presence. They do swim around, so they aren't totally still, and fin health seems good. Hard to see, since tank is polyethelyne. I haven't changed any water yet, but when I do, it is Chicago tap water run through refrigerator carbon filter (plus 24hours of aeration to make sure chlorine is out).

Nitrite spikes are always a bit slower to pass.  To help mitigate nitrite toxicity you can add sodium chloride (salt) to the system to 1 ppt though it might be a bit late to do much good.  Anyway, here is a link that would give you more details about the salt

Now I hate seeing anything but 0 on my nitrite readings but changing water is more likely to slow the progress of cycling past this secondary spike so it's a hard call.  What type of system is it? What method are you using for the media bed, timed or siphon or constant flood?  If you are doing timed, you might run the pump constantly for a day leaving the bed constant flood for the day and see if that has an effect on your nitrite levels.  If you are running a bell siphon you might get the same effect by pulling the bell off for the day.

Great suggestion TCL. I had a similar phase in my newer system - I slowed all of the GB fill rates to the minimum required to engage the siphon for several days. Basically, the same strategy - give the bacteria a little more time to do their job.
One note Claude - IMO, as a general rule, any nitrite level is bad. Tough fish can tolerate to some level, but then a human can tolerate some level of cyanide before it finally kills us, right? Either way it takes it's toll. I've been told the damage is often permanent.
You made a big change when you moved the fish and a dozen 6 inchers would rock a 60 gal FT initially as you saw with the initial spike. Sounds like you're on track to a healthy balance.

Thanks for the suggestion TC! I have a continuous pump w/ bell siphon. I just popped off the bell and the bed is now full 100% of the time. I'll see what happens to the nitrite level tomorrow. I agree Chip that a dozen fish was maybe too much to start right off with. There is a decent size distribution among them, but overall it was probably too many. I'm just surprised that the nitrite's not processing through given that I haven't fed them for 5 days now.

But they're still swimming around, so maybe they'll survive. It's been 4 days of about 1ppm Nitrite now.

Even if you are not feeding them, they are still giving off some ammonia and in a new system the nitrite spike is usually the hardest to get past.  Here is sending good wishes to your fishes.

TCLynx-But his system isn't that new, and it has been cycling 2-4ppm tan to no3 in a day.  Un-feed fish are not going to be adding that level of ammonia.  At least I think they won't.

My bluegill were always very shy compared to other fish, and getting them to eat at first was a chore.  I mixed wild bluegill with farm raise hybrids, and the hybrids convinced the wild ones that pellets were good.  Since you moved them from another system that I  assume was pellet fed they should go back on pellets with relative ease.  I am always harping that fish do not need to eat like we do.  In fact, I stopped feeding catfish in the cooler months down south for 3-4 months, granted the water temps were low and therefore metabolism was low.  So going a week or two is not going to be a big deal.

BTW both folks above are correct.  0 is best, but depending on the fish species levels higher than that are acceptable.  Largemouth bass for instance can live in high levels(160-200ppm) because nitrites do not accumulate in their body.  Apparently according to this review paper bluegills are also insensitive.

Happy reading:

Hi Matthew,

Well, I guess I learned something today. I have Tilapia and Koi and they are vulnerable to nitrites. Regardless, I'd hate to have to remember which fish/FT can have Nitrites present and which can't. Like you said, a big fat "0" is best.

You mention his system not being that new, actually, it was brand new - brand new to fish. Doing fishless cycling doesn't mean you can drop anything in the tank with no issues. Claude said himself said it might have been a bit much for the 60 gal tank. I'm not sure what ammonia source he used or how much/how often he introduced it, but a bacteria colony obviously formed and was managing the system. A dozen 6 inch fish may potentially present a greater load than the system was balanced to handle. Personally, I always cycle with fish because once the cycle is complete and it's time to move fish in or out, I have a feel for the current load capability. That's why I have Koi growing big and fat in both my large tank and pond. Kind of attached to them now and you know, I've never lost a single Koi to cycling.

TC mentioned the Nitrite spike being slower to pass. She also mentioned how salt can help if you are anticipating a Nitrite spike. In addition, I really push the DO level. I have spraybars on both my AP tanks, in additon to my GB's dumping directly into the FT's. My breeding tanks have heavy aeration as well. Getting the DO up can really help manage through the hopefully rare, ups and downs.

Regardless, it sounds like Claude and his fish will be fine - please let us know when things get back to normal.

Removing the bell siphon for 12 hours didn't seem to change Nitrite levels much, although I'm sure it helps. I do see trace ammonia levels again at 0.25 or 0.50 ppm, so clearly the fish are producing ammonia unfed. I don't see any dead fish or rotting material (unless it's in the grow bed), and water is clear, so it must be the fish.

I guess all I can conclude here is that 12 unfed bluegill are too much for my system right now. On the other hand, they seem to be tolerating the conditions, so maybe given some more time my bacteria will catch up. I had just thought I would have more capacity than that.

As always, thanks so much for the advice and support. There's nothing like unexpected behavior to spur learning! I'll post an update if conditions change.

Hey Claude,

Is this the same system that less than a month ago had an unknown nitrite level (in excess of 5ppm, which is the highest reading your kit will register), and ammonia levels also unknown, above 8 ? Did you do another water change? Or did the ammonia and nitrate levels come down themselves, allowing you to dose to 2-4ppm ammonia and be at 0 ammonia the next day? 

Yes. Late Nov. or early Dec. I had overdosed the ammonia. Mainly because I failed to follow the test kit instructions, but also because I had actually overdosed it even before testing. I wound up doing 3 or more full water changes. Even though I changed the water, the ammonia would leach out of the hydroton and build up to 8ppm+ levels. Once thoroughly flushed out (and after I read test kit instructions), I was able to slowly build up ammonia and after about 35 days I had a fully cycled system processing about 2-4ppm per day down to zero ammonia and zero nitrite.

So, I don't believe my problem is due to past ammonia overdose. But it is puzzling that these fish can produce so much ammonia (and then nitrite) without being fed for 5+ days. They might have been heavily overfed in their previous tank (at least, that's what I heard).

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