Tilapia died without obvious symptom

[Amy Lu]

I am Amy from Southern California. I have my AP system for almost three and a half months now with one IBC tote as a fish tank (~200 gallon). I only have 11 fishes, so the density is not a problem. This week I already found two dead fishes about 4-5 inches without any symptom (scale looks fine). The water quality looks good (PH: 6.4-6.6, Ammonia: 0.25 ppm, Nitrite: 0 ppm, Nitrate: 0 ppm). The water temperature is 62F-66F. Is that too cold? I noticed that the fishes don't eat much. In the summer I feed them 2-3 times a day, but now only one time a day. I want to add more fishes to the system for the benefit of plants, but I need to solve this pronblem first. Any advices are welcomed and highly appreciated. Thanks!

[Amy Lu]

Thanks Randall. I do not scoop out uneaten food since they normally will finish it later. I will only feed them if most of uneaten food has gone at the bottom of the tank. I am not sure what kind of tilapia I had. I just emailed the guy who sold them to me. The only thing I can think about is the water temperature. Currently, the temperature is 52F-85F outside. I have already used a 300W heater which can only maintain the temperature around 62-66F. I plan to add another heater.

[Hank Paloci]

I am also in SoCal near the ocean. My guess is water temp is too low.

I've experimented. I lost fish this summer when I had a tank outside feeding my outside grow beds. The temps just get too cold at night even in June.

I keep my tanks in my garage and pipe fish water outside to the grow beds. This keeps my tank water temp higher and more stable, and even though the garage isn't insulated for people it reduces my heating costs. I'm really sure I've created a situation that is stable year round - no need to winterize like a lot of folks.

Also, I think pH is too low for the fish. Tilapia will live at that pH but they thrive higher, I think. Consider raising pH to reduce the stress.

Hope this is useful.

[Cornelius Michél du Plooy]

Hi Amy.

I'd agree with Hank. The temperature should not be below 68 for Tilapia. I have a system in a hothouse with a heater to control night temp. My water temp stays between 68 - 78F.

But! I would also like to know more about keeping my fish alive. I don't have a high mortality on my fish, but still too high to my liking. I feed them pellets supplied by the nearest fisheries, but the pellets smell like fish. I'm wondering whether the fisheries use fishmeal to add protein to the diet. 

Something is also coloring my water dark. It forces me to do regular water changes. I suspect the pellets. Maybe overfeeding.

I have an ebb & flow with gravel, a direct flow with gravel and a DWC grow bed in the system.

Your input would be valuable.

[Steve R]

what is your alkalinity? also called KH? if it gets too low like might happen if your PH is stabalizing tha low then it will fly around during the day and could potentialy kill them through ph shock. 

[Amy Lu]

Thanks Steve. How can I measure the KH? What affects KH? If that's the problem, how can I fix it and keep it stable? The FT water starts at PH 8.8 and within three months it drops gradually to PH 6.4. Currently I have used some egg shells and limestones to try to stabalize it. Thank you so much for your inputs!
 
steve raisner said:

what is your alkalinity? also called KH? if it gets too low like might happen if your PH is stabalizing tha low then it will fly around during the day and could potentialy kill them through ph shock. 

[Amy Lu]

I may not be experienced enough to give you useful input since I am a beginner too. What color if your fish tank water? The only thing I can think of is the algae. I had algae grown in my FT at the beginning and it is kind of dark green color. Then I covered my FT with black mesh which blocked most of light. Since then my FT water remain clear. You didn't use Maxicorp, right? Maxicorp will turn your water to black and it takes about two weeks to clear out. I assume if you feed them to much, you will get a lot of waste sediment at the bottom.
 
Cornelius Michél du Plooy said:

Hi Amy.

I'd agree with Hank. The temperature should not be below 68 for Tilapia. I have a system in a hothouse with a heater to control night temp. My water temp stays between 68 - 78F.

But! I would also like to know more about keeping my fish alive. I don't have a high mortality on my fish, but still too high to my liking. I feed them pellets supplied by the nearest fisheries, but the pellets smell like fish. I'm wondering whether the fisheries use fishmeal to add protein to the diet. 

Something is also coloring my water dark. It forces me to do regular water changes. I suspect the pellets. Maybe overfeeding.

I have an ebb & flow with gravel, a direct flow with gravel and a DWC grow bed in the system.

Your input would be valuable.

[Cornelius Michél du Plooy]

Thanks for the input.

[Hank Paloci]

Sometimes we overthink these things. Stuff usually grows with minimal interference by people. I pulled a 4 foot tall basil *tree tonight and made pesto.

I never check KH -- it's a necessity in many places but pretty sure I don't have to, using treated LA tap water.

I really think that if you just raise the temp in your pond you won't lose so many fish. Just keep it simple.

[Steve R]

It's mostly likely the temperature but if everything else checks out its the next place I would look. You can get a kh test kit at any pet store for under 10 dollars. Low kh isn't common but i have seen it being the lethal issue when all else checks out fine. If your alkalinity gets to low it destabilizes your PH and it can raise or lower alot over a 24 hour period. The strangest fish die off i have ever solved was in a dentist when i used to work on aquariums. this dentist had a fish tank that could not keep fish alive more than a few days he hired 3 company's we were the 4th trying to figure out why his fish would die. everything checked out fine in water tests i brought water with me from out facility to make sure all variables were accounted for put a web cam on the tank to make sure it wasn't a person and couldn't figure it out. They were about to fire us and finally I got frustrated and thought I wonder whats in the walls near the tank. So I start opening the cabinets and push around the ceiling tiles above the cabinets where the tank is. WELLL it turned out they had some electrical work done a few months back and the nitris oxide tanks and oxygen tanks were in that room and had lines that went to the individual dentist stations and the electrician had nicked one and not noticed and the poor fish were getting gassed in the tank. So you never know when something odd or strange can be the culprit always start with the basics and think of all possible variables even if its not obvious at first.

[Cornelius Michél du Plooy]

Great perspective given Steve.

My makeshift pond is an old bathtub. Since I lined it with pondliner, my fish mortality decreased. Seems something in the tub seeped into the water, poisoning the fish. But my mistery is not completely over, since I still loose about 1 to 2 fish per month. I decided not to purchase more fish, untill I'm sure what kills them. Due to that decision, I have only 10 fish in a 650 litre system. Giving low nutrients and keeping the pH above 7, below 8. (due to little nitrification).

Do you think anything in what I said could contribute to my problem?

[Amy Lu]

Steve, you are right! I used the strip to check KH and it is very low (~40ppm). I have ordered Potassium Bicarbonate and Calcium carbonate. Although the KH is low, the GH(total hardness) is high. My tap water is very hard (300 ppm) with PH about 8.8, so I never thought KH in the FT can drop that much. After doing some research online, it is normal the KH drops with nitrification process. I am wondering why other people haven't encounter that problem. Is any simple way I can use to keep the KH stable?
 
steve raisner said:

It's mostly likely the temperature but if everything else checks out its the next place I would look. You can get a kh test kit at any pet store for under 10 dollars. Low kh isn't common but i have seen it being the lethal issue when all else checks out fine. If your alkalinity gets to low it destabilizes your PH and it can raise or lower alot over a 24 hour period. The strangest fish die off i have ever solved was in a dentist when i used to work on aquariums. this dentist had a fish tank that could not keep fish alive more than a few days he hired 3 company's we were the 4th trying to figure out why his fish would die. everything checked out fine in water tests i brought water with me from out facility to make sure all variables were accounted for put a web cam on the tank to make sure it wasn't a person and couldn't figure it out. They were about to fire us and finally I got frustrated and thought I wonder whats in the walls near the tank. So I start opening the cabinets and push around the ceiling tiles above the cabinets where the tank is. WELLL it turned out they had some electrical work done a few months back and the nitris oxide tanks and oxygen tanks were in that room and had lines that went to the individual dentist stations and the electrician had nicked one and not noticed and the poor fish were getting gassed in the tank. So you never know when something odd or strange can be the culprit always start with the basics and think of all possible variables even if its not obvious at first.

[Steve R]

To Amy LU   http://www.aquavitro.com/products/carbonate.html you can use a product like this one containing potassium bicarbonate or if you have potassium carbonate from our PH up kit that can also be used but again won't be as effective as potassium bicarbonate. Alternatively you can get it in 50 pound bags at most pool supply stores. I have also read a few posts recently with people using crushed coral mixed with there grow media to maintain. PH and alkalinity but i myself have yet to try it but it might be soemthign worth looking into.

To Cornelius have you replaced all grow media and pourus materials from your system since you changed the liner? It not what ever chemical that had leeched into from your tubs is now in your grow media and pouris materials and is leeching back into the system. You need to replace anything that it might have leeched into. Alternatively depending on the chemical that was the issue it might have already damaged there organs and is just taking its time to kill them with out knowing what the chemical was i have no way of knowing.  If its a old tub tho i can't imagine anything other than hard metals or soaps but neither would be at all likely are you sure that was the source of your motalitys? What is your water chemistry? Tell me a little bit more about your system.