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We have a 500 gallon system that had been fully cycled/established for a few months without fish.  We added tilapia fingerlings last week.  They have been doing great, eating like crazy.  This am there is a nitrite 7.6 (normal for this system) ammonia 2 (little high for this system)  nitrites 5+ and nitrates 80 .  During this week, while adding water to system, it was left on too long  and there was probably about 50% water change.  That happened about 4 days ago which was about 3 days after the fish were added.  My question now is how should I address the spike ?  Do I change out some water ? Add Salt ?  Do nothing ?  The fish seemed fine this morning and until I read the forum, did not realize I should stop feeding them......what else ?  thanks

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I would change water, then salt.  If you see nitrites going down, resume feeding, perhaps once every other day to start.

George.......looking at forum, I cannot find clear recommendation for amount of salt I would add to 500 gal system.  I have epsom and sea salt on hand......please advise.....if the sea salt is going to hurt my plants, I would almost rather take the fish out for a while and let it come back on it's own if they can handle the stress.

George said:

I would change water, then salt.  If you see nitrites going down, resume feeding, perhaps once every other day to start.

Plants can tolerate a certain amount of salt.  See the link.


George said:

Plants can tolerate a certain amount of salt.  See the link.

My system is only about 1 month old (150 gallon fish tank, 85 gallon grow bed with expanded clay, 25 talapia fingerlings), but the ph in our area is 8.2.  I was worried about that until I read in the booklet that came with my water testing kit that 8.2 is ideal for african cichlids, which I believe my talapia are.  But everyone seems to say that 7.5 is the ideal for aquaponics in general.  Input anyone?

Meanwhile -- both my nitrites and nitrates are off the charts.  Ammonia is barely detectable.  I've done a 1/3 water change and both nitrites and nitrates are still high.  Input?

Actually 7.0 or less is good for pH. Experts say 6.5 for plants and fish is a good compromise. I'm not an expert but if you're getting Nitrates then your bacteria are working. Depending on the age of your system the Nitrites should be close to 0 once everything has cycled. How old is your system? A great source of real information is Bright Agrotech on YouTube. Nate covers all aspects of aquaponics. 

You said your readings are off the chart. I just picked up on this recently. Either double the amount of water or cut the number of drops in half and do your measurements that way. Then what ever reading you get just double it. I had to do mine times 4. My nitrates were over 600.

It's normal - good in fact - add ammonia (more fish) and nitrite should rise - your nitrosomonas is increasing and producing nitrite from the ammonia ...

First, your system can't be "cycled" without fish - you need the ammonia for the nitrosonomas population to have ammonia to eat, thus to produce nitrite.

You need nitrite for the nitrobacter to have something to process into nitrate.

The populations of these bacteria grow to meet the availability of food (as all populations of anything do) but they lag behind a big jump in food availability.

You should attempt to run your pH closer to 6.8 - optimum plant micro-nutrient uptake is in the range 6.5 to 7.0. People on the forum are probably going to jump up and down with their own opinions but it is what it is .... nutrient knock-outs occur outside of this range ....

5.0 nitrite is high, but the fish are pretty tolerant of nitrite ... and the nitrobacter should knock it down in a day or two if you have a properly designed & sized environment for the nitrifying bacteria to do their work (needs lots of oxygen)... it's ammonia that will get your fish - look into ionized vs un-ionized ammonia - ammonia vs ammonium - you need to understand the difference to know what can do fast damage - the ratio of the two ammonia forms and thus toxicity to fish are controlled by pH and temperature ... ammonia to fish is like carbon monoxide to people - it can saturate their blood and their body chemistry can't expel it ... then they are goners.

Try not to shock your system .... dont swap half the water if you can help it -

have fun - hope all is well


pH is important, but I don't recommend chasing numbers, it's a difficult battle. pH will come down on it's own in time, BUT high pH and hi temp = hi toxic ammonia. Salt is good as it blocks the uptake of nitrite in the fish and prevents brownblood condition. However this is most effective BEFORE the nitrite exposure, though I would still add 1 oz per 5 gal as a start. KCl ("sea salt") is good. Epsom salt is good to add to the mix for plants, but does not have the Cl ions to aid with nitrite for the fish.

By the way, I always cycle without fish using ammonia and I have made the same mistake - you need to continue providing ammonia for the bacteria until the fish are introduced. Even then I always seem to get a spike after adding fish and I go through a nervous period. Patience is hard when your fish may die. But make as few changes as possible or things can get out of control quickly. I usually make sure I have about 2% salt in my quarantine enclosure to help with the nitrite spike and then I raise it as needed to fight disease like Ich. I use a portable refractometer to measure salinity and I go up to 6% to fight disease but some fish won't tolerate salt above 4 or 5%. Tilapia are tough though, they are hard to kill.

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