Backyard Aquaponics
A place to discuss aquaponics

My system has had high nitrites and I dont know how to lower them. I saw a catfish at the surface today which scares me. So far I have not lost any fish and I want to keep it that way. I have 32 catfish and 7 bluegills in about 1400 gallons of water. I only have about 100 gallons of filtration. The water temp has dropped in the last week and is around 42 deg F. I have been feeding about 10 grams of food a week and adding some humonia. I have not added anything is about 2 days. I have not salted my system at all because my alkalinity has been high. How can I lower the nitrites? I am doing some water changing but can only change about 50 gallons a day.

How high is high? What about ammonia and nitrate? Was the system already cycled or are you in the middle of cycling?


Do you have supplemental aeration in the tank? Air pump and air stones? A fish tank that size could have 3.5 cfm of air going into it.
Ok so that is almost 40 fish in a huge amount of water, how big are the fish? How long ago did you put them in?


Oh boy!!! There could be an issue.
First, what sort of filtration is it? Is is a flood and drain gravel bed? Or is it some other type of filter?
With 100 gallons of filtration (of a flood and drain gravel bed type) I would only recommend 20 fish and only if their final grown out size is about 1 lb each. Basically, 100 gallons of cycled flood and drain grow bed should be able to handle filtering for about 20 lb of fish. I have the impression that your system is not cycled up yet and therefore you are overloaded and under filtered.


The cold water has also probably stalled the bacteria a bit and the fish probably should not be getting fed at that temperature.


I again want to know what your other test results show. I never recommend adding humonia to a system with fish in it unless it is already very well cycled and there just isn't enough nitrogen to support the plants cause the fish are not eating.
At this point Stop feeding and don't add any more humonia! do not feed again till both the ammonia and nitrite levels drop. Don't add any more humonia as I expect you have overdosed.
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I'm not quite sure what salt has to do with alkalinity. You need at least 1 ppt of salt (sodium chloride) to help mitigate the nitrite toxicity. That would be 1 kg of salt per 1000 liters of water. So for your 1400 gallons that equals 5300 liters, needs 5.3 kg or 11.7 lb (12 lb would be fine, catfish and bluegill are both ok up to 5 ppt of salt but I don't like to salt my system past 3 ppt) When adding salt, avoid table salt as the anti-caking agents are not good and neither is the iodine. You are better off getting solar pool salt or solar water softener salt (it's just sun dried sea water) it comes in like 40 lb bags for around $6 and dissolving it in buckets of system water before adding it back into the system. You do not want to simply throw the salt crystals into the fish tank as they will tend to sink to the bottom and take a long time to dissolve, if the fish rest against the salt crystals on the bottom, they will be burned by them.

How to lower nitrites? Water changes are the only fast way to do it and 50 gallons a day will probably not make much difference in 1400 gallons of water and if you are changing with treated water, you are probably better off not bothering. You need to get cycled up. How high have the nitrites been for how long?

Get the salt in ASAP, make sure there is plenty of aeration (not only to assist the fish but also for the bacteria) and don't feed or add any humonia until the nitrites drop. You will also need lots more filtration soon.

_________________
Aquaponic Lynx
TCLynx Bought The Farm
Old Main System
Old 300 gallon System

I will go get some salt. I have no way to test ammonia but nitrates have been fine. I only have quick test strips and they indicate nitrite 8-10. I have about 50 gallons of flood and drain and 40 gallons of continuous biofilter about 700 gallons per hr. The biofilter is well established about 4 months 2.5 with the fish. Half of the grow bed area is 2 months old and the other half is 2 weeks old flooding for 15 min per hr. I also have some floating growbeds. I have treated water so thats why I cant add much. I have to let it breath for a day to clear out the chlorine. The temperature has dropped rather rapidly in the last few days and I think that may have caused the spike. I have a good air pump not sure of the cfm but I figure about 50 lpm. I run it for 30 min per hr. Thanks for the advise.

Ok, went and had a look at your system thread.

So is it 50 gallons of upflow bio-filter and how much flood and drain gravel?

Can you add a huge amount of extra air down into the bottom of that bio-filter? I mean make the thing boil with air?

See I'm currently experiencing a sorta similar problem with an aquarium system and nitrites. (now I have not let the nitrite get high-perhaps up to one for a day or two- and I do have salt in there and the fish are tilapia so can survive much that will kill a catfish or bluegill) Anyway, even with air stones in each of the three up flow filters I have hoked up on that aquarium, the nitrites are not going to 0 yet and it has been cycling for weeks with 74 degree water.

This is something Rupe often comments on, constantly flooded filters tend to have nitrite problems or in other words, a flooded filter can't support as much bio-mass as the same volume of flood and drain filter.

That aquarium system I was mentioning, has an equal amount of up flow filters as there is fish tank. About 9 gallons of fish tank and at least 9 gallons of filter and I still haven't gotten the nitrite to drop to 0 (though I must admit I haven't completely quit feeding as they are young tilapia and would eat each other.)

Anyway, I think your best bet for reducing the nitrite will be add as much more flood and drain as you can and bubble as much air as possible into the system.

_________________
Aquaponic Lynx
TCLynx Bought The Farm
Old Main System
Old 300 gallon System

If you can, I recommend getting this type of test kit.
http://www.thatpetplace.com/pet/prod/199591/product.web

The test strips are generally not considered very accurate.


Run it full time till the nitrites drop

So have the nitrite levels been fine up until just after the temperature drop?
If so, then you are probably right that the chill did it. The bacteria that convert nitrite to nitrate are generally more sensitive to temperature than the ones that do ammonia.

Then again, what is your current pH? Since you can't test for ammonia you are kinda blind. Another thing that commonly happens to systems that have been up and running for a few months is the sudden pH drop that if not buffered against can cause a crash and ammonia spike. If the pH gets way too low, the bacteria that convert ammonia to nitrite can suffer. Bummer here is ammonia becomes more toxic as you increase the pH but the ammonia won't be converted if the pH is too low. Anyway, I'm not thinking that this is your problem since you have the high nitrite and it seems to have been temperature related.

Any reasonable way to warm things up a bit? Gonna be a hungry winter for those fish if it stays cool for the next two months.

_________________
Aquaponic Lynx
TCLynx Bought The Farm
Old Main System
Old 300 gallon System

I had a solar heater but I blew a pipe and havent fixed it yet. I will put the air bubbler into the biofilter. I dont have a good way to add more grow beds because of space limitations. current ph about 7 I have a bag of oyster shells in the flow from the pump output to help buffer.

Yep... salt to 1ppt.... more air in your bio-filter... and no more hummonia...

Ok I got that biofilter boiling with air now. I also put in 2.5 kg of salt. Can I add all the salt at the same time or should I stretch it out over some time?

All at once...

5.5 kg salt in and filter boiling. I will report back tomorrow with results.

How are the fish doing? And for how long has the nitrite been high?

Perhaps you could pump some water through some black tubing during the day to help raise the temp a little, the whole setup is under greenhouse plastic isn't it?

_________________
Aquaponic Lynx
TCLynx Bought The Farm
Old Main System
Old 300 gallon System

its all under a greenhouse. The fish seem fine. Hard to tell I will only see them if they come to the surfac. I saw one yesterday but when it saw me it went back to the bottom. I have alot of algae in the tank and dont see the fish much. The nitrites have been high for about 3 days that I know of.

nitrite still high. I changed some of the water and will do more tomorrow. No dead fish yet.