kribensis12
I know where you live
I think your temperature is too high.
You can only set to 87F high for Discus that are sick and not eating.
For Rams, you can set up to 85F.
86F is for treating ich if the fish can withstand the heat.
For other fish, it should be below 85F in my opinion.
Warm temperature will reduce the oxygen level. If you have many fish, the tank may also run out of oxygen.
If your thermometer is malfunctioned or not accurate, you could be roasting your fish.
Watch this video:
Anyway, any mass dying or fast dying of fish means you have toxic in the water or bacteria such as Columnaris that can kill them fast or you are altering the water GH, pH.
Bacteria will kill faster than parasites.
For any toxic in the water, just change 100% of water will solve the problem.
You can also use carbon if you suspect something is continuously leeching toxic.
By the way, did you alter the GH, pH?
I heard of a few cases of fish dying quickly due to altering the water pH.
pH should not change more than 0.5 or 0.2-0.3(for sensitive fish) in 24 hours.
For how to save fish affected by toxic, you can also watch the below video from 9 minutes onward.
@Lajos_Detari I appreciate your perspective. I would counter that 87 is not too high - I am connected to several highly experienced breeders who breed Rams (all 4 color varieties) and they raise the fry at 87 and a former Mod on this forum, "Tolak" used to breed high-end Angelfish by the 1000s and he raised all of his fry at 87. My digital thermometer is accurate - I just calibrated it.
The mass dying to me does indicate a toxin but as I mentioned previously, I don't know what it could have possibly been? And to happen 2 separate times?
In relation to kH and gH, I do not have a tester for it but as I handled the water change as I also do (without incident in 7 tanks for years) I am thinking that it is unlikely. It could be possible though - clearly something went very wrong. The rams got moved into a tank with much softer water (out of necessity because obviously something went very wrong) and they seem to be a LOT better.
First off I used to breed large numbers of Apistogramma cacatuoides. Any pair in a 10 gallon is facing death from stress. The tank is too small for their needs, and I would almost expect what happened.
Cacatuoides will die at 87. Rams come from sunlit Llanos habitats, basically savannahs, and they have adapted to hot water. Apistos are generally from more shaded forest habitats, and I bred and raised them at 25-26C max.
Second, the ram fry do tend to die easily, as a delicate species. But you must maintain water stability with fry. Pure RO? Did you change the hardness of their water and blow out their kidneys? That's a blackwater species from almost pure water, bred to tolerate soft tap water and to survive in harder tanks. But any bounce around in hardness levels can kill fry.
I disagree here - I have a breeding pair of cockatoos in a 10g who have been cohabitating successfully for one year with about 12 successful spawns. If you read the thread I linked, it is very obvious that the tank size is not related to their deaths whatsoever.
I do agree that 87 is too hot for Cockatoos - which is why, in my post, you'll see that I do not keep cockatoos in 87 degree water.
Rams are very delicate, correct (I breed black rams too and they are very very delicate). I did use pure RO because I noticed my TDS was higher than I'd like and the water change dropped the TDS by 50 (which would include kH and gH) which is not a huge drop. I do this occasionally and have never had a negative outcome from it - and their symptoms don't seem to match what I'd expect if I had shocked them.