Question regarding adding fish to restock a 36 gallon

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platytetrafan

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Jan 20, 2007
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Hey everyone I have a 36 gallon tank my water parameters have been fine until recently. Over time a few of my fish have died from unknown causes possibly age and 3 from what looked like a fungal infection which I tried to treat but the fish died despite me trying aquarium salt in a separate tank and when that didn't work tried fungus guard tabs but that didn't work either and the fish died 3 bleeding hearts at different times got injured and then the fungus infection started. I lost a cherry barb 2 cories & 4 danios . These deaths occurred over time and what was strange is that my water parameters were fine all along. I do weekly water changes and check my levels weekly. In my current stock I have 19 fish in my 36 gallon. 3 discus that are stunted I rescued them from LFS they are small but healthy and they are all doing well , 5 cherry barbs, 4 cories, 3 bleeding hearts and 4 glowlight tetras.

Over the last 2 weeks I have been getting ammonia spikes but don't know why? Could I have lost some of my beneficial bacteria because I don't have the original fish load I had months ago? I try not to overfeed I do gravel vacs regularly and water changes approx 50% weekly because I was told discus need very clean water. Yesterday I tested the ammonia and it was at 0.5, today after the WC I did yesterday it was at 0.25 ammonia so I did another 50% WC this afternoon tested the water tonight & it's back down to 0. Same thing happened last week but I got the ammonia level down after doing WC'S. I also added this liquid beneficial bacteria product from Top fin to the aquarium water to boost the bio filter. When I checked the sponge last week I noticed it wasn't as gunky as it has been which has me worried. I realize I have to get my 10 g QT going and replace the number of fish that died.

My next question is once those fish go through the month of QT & hopefully stay healthy how many fish should I add back at a time I know it has to be done slowly. I don't want to overload my bio filter I know it has to gradually adjust back to the number of fish I originally had in the tank. Any advise is appreciated.
 

NoodleCats

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Discus are higher bioload fish and are being kept in too small of a tank--your filtration can't handle the bioload in the capacity of tank you have.

Another issue is temperature compatibility which can cause problems too.

Discus need very warm, well into the 80s to stay healthy.

Cherry barbs, danios, and most corydoras need it cooler, below 77F usually. Sometimes lower depending on cory species too. Danios and cherry barbs still do better longterm between 72-75F but can go to 77F. But any higher causes problems. Danios especially I notice, constantly gravid in the hotter temps and this causes bloat problems in the females.

Keeping the cool water fish too hot will stress their immune systems and make them more prone to infections.

Keeping the warm water fish too cold will make them lethargic and too stressed to function properly to enable a proper immune system as well.

This also affects lifespan too.

I would get a 75 gallon minimum, ideally larger if you can for the Discus, keep them in a warm tank and on their own. They're schooling fish as well.

Keep the barbs, danios, tetras, and the cories in the 36 at the temps they need.
 
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platytetrafan

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Thank you for your reply. I know that discus of larger size should go into a much larger tank than my 36g but I don't have the room for a 75g these guys were stunted I bought them from my LFS and they are smaller than the much bigger size discus. When my tank was fully stocked I was having no issues at all everything was fine but I started to lose the fish I described above over time the bleeding hearts I know were pecking at each other and I saw the nip marks from where they were nipping each other and then the fungus infections that I tried to treat one by one didn't work so I lost 3 due to that issue. The cherry barb that lost his eye lived for months after that happened I never knew why he passed or what caused the injury in the 1st place. The danios also lived in that tank a long time with the discus and the cories as well. My tank temp is at 86 and until I started to lose fish some for unknown causes other than the cherry barb and the bleeding hearts everything was fine the fish swim eat well and play and although I understand that some fish prefer temp at 77 I had the tank water temp at 82 and the fish were fine. My biofilter was filled with bacterial medium but I noticed in the last two weeks that alot of the sludge is gone and that could be the reason for the ammonia spikes because the number of fish I originally had in the tank is not what I have now. There are 19 in the tank including the 3 discus.

I am planning to QT some new fish to add back to the 36g to bring the load back up to what I originally had to replace the ones I lost but wanted to know once I do that and know that the fish are healthy after a month's time how many should I add back to the 36 g tank at a time?. I don't want to overlwhelm the filter since I know it has to build back up overtime. Thanks for the advise I appreciate it. The water quality as of yesterday is back to normal and am keeping an eye on it and trying not to overfeed and continuing WC gravel vac as I was doing on the 36g.
 

NoodleCats

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The fish are weakened by the hot temperatures, get them a separate tank and cool it down for them, otherwise they're going to continue going downhill.
Unfortunately.

The heat puts stress on their immune systems which will make them prone to problems more and more when healthy fish would fend it off.

Keep the discus separate.
 

fishorama

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You know I think we've discussed this of yours tank before. A 36g is not large enough for 3 discus, even stunted, let alone with all the other fish. ...& as NC said temp incompatible. I'm sorry to pile on, but you need to rethink your tank's future.

A 36g is suitable for a breeding pair of discus without other fish...or a very few that can handle 82F, not 19 others of any kinds. Your tank is just too small for all those fish!

A pair of stunted discus "might" be able to breed & if there's a male & female they will try, there's no way to stop them. But having all their organs stuffed into a too small body can mean trouble especially for females, eggs take up some room no matter if they're stunted. You've given this combination a good try...it's time to move on to a more sustainable tank. I'm sorry.
 
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