Disaster struck Monday night as I lost a full adult G. sveni and a L56y, both my favorites. I ended up spending all night draining the tank and cleaning the DT and the sump. I found out a small piece of twist tie in the sump, which made me think it could've been metal poisoning? It's been over 24hrs since Monday night and there were no casualties--I was getting at least 1 casualty per night for the past week. I'm monitoring the tank and hoping it was simply a case of bad luck with a loose twist tie.
I find it hard to believe that one twist tie could poison a 300 gallon tank plus sump. Especially to that extreme level where every night you're getting another casualty. Unfortunately I don't think you found your problem. Or fixed it unknowingly.
I agree, the idea it was a twist tie that caused the deaths is very remote, even if the metal was corroded, I have found rusty screws in tanks over the years that have fallen off rusty shop lights many times.
Check the light on the tank on the left.
There are any number of diseases that can lay dormant in a tank, and infect new comers.
This is why in many threes I stress a 3 month quarantine, not only to save old tank inhabitants from something the new fish carry, but some latent bacteria the old tanks fish have developed immunity to, but new fish haven't, or water conditions new sensitive fish are not accustomed to.
You guys are correct, I found the issue and it wasn’t the twist tie. More Sveni died—4 adults—last night and I found a rotting carcass of a pleco. I did a test and was surprised the ammonia still read zero with water smelling foul, so I went to buy another test kit. Turned out the nitrite was testing wrong. I have to my amazement still 0 ammonia but 2.0 nitrites, which explains the S. papaterras gasping for air prior to their deaths. I’m doing a fin level water change right now and got myself 4 bottles of Tetra SafeStart plus.
I think the tank went to a cycle after the furan-2 and kanaplex treatment a month ago. I did get lucky a bit with my 2x a week huge water changes since I think it prevented more deaths. Also, feeding only every other day helped keep the bioload lower.
The fight is not over, wish me luck. I’ll keep you all posted. Thank you for your support and help.