Hello,
First of all I want to congratulate Nicole with baby born. Well done!!!
Then I want to thank the forumers who advised me "long-playing" feed for my fishes which worked perfect while we were in Florida for 2 weeks. That thing dissolves in the water and bit by bit feeds fishes.

But now I wonder: the summer is extremely hot, so what should I do to prevent the water in the tank from warming up? I know that goldfish are pretty tolerant to jumps in temperature, at least that's what I was said in Petco, but still. I don't have any thermoregulation in the tank, nor I have thermometer. So far the fishies look okey, but today when I was making a regular water change, I noticed that the water in the "cold" tap was lukewarm. I would prefer to have really cold water in a shower in such weather. May be the same would prefer the fishes, I thought.
What you say?

I say the fish will be fine in warm water and just leave them be.  They will adjust or adapt to the water temperature.  Goldfish can tolerate 90 degree water all the way down to freezing.  What they can't tolerate is constant water temp changes.  It causes stress.   My goldfish tanks are all in the eighties and they have been just fine.

Higher temps in the summers are a small thing that's natural for goldfish that live in ponds and the like, and it usually triggers breeding behavior So I'd wish that all the people who keep making threads about "hot" water in their tanks would chill and leave it be xD