That Is a bad thing. I don't like the idea of such a clean tank; what I keep, is a clean "looking" tank that is actually alive with "dirt" (aka, beneficial bacteria and algae.)
Goldfish do thrive better in cooler water.. my two GF tanks are purposely kept in cooler patrs of our house for this reason.
For my Gfish, I love the Hikari pellet food; seriously I think it makes them grow a bit better and get better colors (though genetics plays a huge part.)
I love Gfish, HATE the rap they have as "kids' fish" that live in a bowl and die fast. Let me post a few shots of mine!