Your fish probably have it. By taking the fry to your 55, that tank now has been exposed to ick too! Watch your fry very carefully. You may be wise to treat both tanks right now - and I know that is expensive with the 55.

70 degrees is ok for the goldfish, though they might "prefer" something a little cooler in the winter. It really is too cold for guppies and probably chilled your fish so that they caught the ick.

If you can verrrrrry gradually tweak the heaters up so the tanks increase in heat 1 degree ever 12-24 hours, your guppies would be better off at 77-80 degrees F. in a couple of days. Guppies normally are best off 75-77 degrees F, but the threat of ick may require the warmer temperatures. You don't want to shock them raising temperatures either.

Don't sell you fry or adult guppies short. Given a chance, they can be pretty tough.

Your Mom is being most gracious in offering to get you more fish. Please don't get any though until the ick is cleared up. You may otherwise just be sentencing them to death. (They also, usually need it warmer than 70 degrees.)

In the meantime, it gives you a chance to shop around for what you would like to have in that tank. Please swing by your public library and find their aquarium books. Read up on the needs and compatibility of the fish you might be interested in.

As for your goldfish, the four of them, all by themselves (or with that tetra), would prosper in that 55. They might very well grow to nearly a foot long, if they are comets. They could live 10 or 15 or even many more years there.

Americans are accustomed to keeping young goldfish in bowls. I've done it too. However it does them no favor in the long run.

In Germany today, it is illegal to keep goldfish in bowls! That is a part of their anti-cruelty law!