I was thinking, maybe since my tank just completed the cycle, the fish is not really used to Nitrates and was acting a little strange? Maybe he needs to get used to Nitrates?
As with Ammonia and Nitrites, Nitrates are toxic to all fish. Poisons and toxic chemicals/byproducts are not something living creatures ever "get used to." It's also not something fish can develop an immunity from through prior exposure. This toxicity is still a health hazard, even while the fish "appears" to be fine. And this is why long-term harm can be done to fish that aren't protected well enough (through frequent enough water changes) when they get put through a "fishy" cycle.
I have a 55 gallon tank with 4 fancy goldfish. They have been doing fine up until now.
Your stocking level is great for the tank size you have. You're doing a fine job of goldfishkeeping, Jim. Keep up the good work!!
Is my tank too hot?
I checked my thermometer and saw that the water is at 74 to 75 degrees. The room I keep the tank in is kept at a constant 72.
I agree with the above. My air went out for a few days last summer and even though the goldfish tank was in the high 80's, the goldfish appeared unaffected.
I would do a water change ASP to reduce the nitrites.
At 74-75 degrees, your tank is a little on the warm side. The ideal temp for goldfish is in the 70-73 degree range. You definitely need to keep the overall temp over the long term at or below 75 degrees. What happens when goldfish are kept above 75 and up into the 80-degree ranges, is their metabolism speeds up drastically and it stays there all the time at a constant level. (Kinda like revving an engine and leaving it there continually will result in higher fuel consumption and a lot of wear and tear.)
This gives us a false impression that everything is just fine because the super high activity level makes it look like they're happy and playful all the time. What we don't see through behavior is how dramatically this higher metabolic rate stresses the fish, preventing them from getting adequate rest periods when they sleep and making them more prone to digestive problems (which is already a huge factor).... to disease, parasites, and other ailments... and how it cuts down their potential lifespan. If they manage to avoid getting sick at this high temp/metabolic level.. they will still sort of burn themselves out and have relative short lifespan. (The same is also true with high quality breeding stock fish that are bred extensively for only a few short years and with show quality fish being prepped, groomed, conditioned, and transported all the time for exhibiting.)
You're looking at fancies that have a 20+ year natural lifespan if kept under good conditions.
