*Hi-five's Ghapy*. Spot on, a 6 month old tank is barely mature, if that had been working for 6+ years you'd be on to something. Goldfish at very warm temperatures over 75F will suffer long term effects and shortened lifespan, not to mention make a hell of a lot more mess than if they were at cooler temperatures as their metabolism is faster when they're warm.
Also, take that Puffer back to the store - this beast is NOT a community fish and will continue to attack, and potentially kill, its other tank mates. It needs to be in a species tank only and will get to a very chunky 6". It is also NOT a freshwater fish - it needs brackish/marine conditions - of which your other fish will not tolerate, Plecos in particular are intolerant of salt. It will continue to attack the other fish.
I would also recommend IDing what species of Pleco you have, there are over 800 species with a vast range of needs. All suckermouth fish may well turn around and suck on a Goldfish's slime coat - which can seriously damage a Goldfish. I would never recommend suckermouth fish with Goldfish.
Also, take that Puffer back to the store - this beast is NOT a community fish and will continue to attack, and potentially kill, its other tank mates. It needs to be in a species tank only and will get to a very chunky 6". It is also NOT a freshwater fish - it needs brackish/marine conditions - of which your other fish will not tolerate, Plecos in particular are intolerant of salt. It will continue to attack the other fish.
I would also recommend IDing what species of Pleco you have, there are over 800 species with a vast range of needs. All suckermouth fish may well turn around and suck on a Goldfish's slime coat - which can seriously damage a Goldfish. I would never recommend suckermouth fish with Goldfish.