You said full cleaning and mentioned new rocks. Did you happen to entirely clean the tank out? If so then your tank is re-cycleing. I would bet what you are seeing as tail rot is actually due to water conditions. You need to test for annonia and nitrite. Wouldn't hurt to test for ph. The fogginess you describe is also common to new tanks or tanks that have been cleaned too well. A 10 gallon tank in the long run is really too small for one Goldfish let alone five.

Lisa

A 10 gallon tank is WAY too small for that number of goldfish. Goldfish are very very dirty fish. I have two comet goldies in a 20 gallon tank and I use two filters because 20 gallons is still on the small side.

Full cleaning can create more problems than it solves! full cleaning removes the bacteria needed to decompose the fish waste, and goldfish put out a LOT of waste. Foggy water is exactly what happened to my tank when I cleaned it too thoroughly. I think it's a bacterial or algal bloom, from losing the bacteria that do the decomposing.

First, get a bigger tank, or lose half the fish. Or both. Then, you want to do frequent small water changes, not occasional big ones. When you change the water, vacuum the gravel and scrub the decorations, and rinse out but don't replace the filter cartridges.

If you have algae problems, you might want to move the tank where it gets less sunlight, or run the hood light for less time. Mine goes on at 3pm and turns off at 8:30. Algae means too much light and too much nitrogen in the water, from fish waste. Live plants would help soak up the light and nitrogen, but goldfish eat them, and algae grow on the plants too in my experience. I've been able to stop using algae killer once I moved my tank away from direct sunlight and put a timer on the hood light.

You need to balance bacteria with fish in a fish tank. That means you need to clean just enough to remove excess fish waste but not so much as to remove too much bacteria. Weekly or every two week partial water changes are best; I remove about 4 gallons from a 20 gallon tank, and rinse the filter cartridges in the water I siphoned out instead of cold tap water, to conserve bacteria living on the filter media.

pH is critical too. pH can shift drastically with a water change. My tap water is buffered to be very alkaline, which many water utilities do to protect the pipes. Fish don't like it. I use a community tank pH buffer tablet to set the tank pH at 7.0. It lasts through a few water changes, but I have to check the pH to make sure it's still working. Otherwise the pH of the tank can go from 7.0 to 7.6 with one partial water change, and the fish do NOT like that. Goldies are supposed to like the higher pH but in my experience they have done best at 7.0. Liquid pH adjusters don't work on tap water that's been buffered by the utility company.

This is a pretty common problem. I'm surprised the pet store you called had no idea. I wouldn't rely on them for advice in the future.

I won't repeat all that is said accurately in responce but to say WAY TOO MANY FISH for such a small tank for gold fish.

TWO repeat TWO smaller fish for the ten and that is it. Period.

(I add emphasis to stress this as I try to stress it with new fish owners who have been sold say 25 fish for ten gallon or even CARP! and come back into the store and want more as they are dying. The pet store could care less as long as they make a sale. One guy was sold huge plecos along with his goldfish (over stocked) and worried that his son would notice them missing so wanted to add more! I said, that' life (remember some of our parents grew up on a farm) and the kid would be more upset when they all died, and that them dying meant something was horrible wrong = 25 fish in ten gallon!

So not sure how it was sold to you, and/or that you did not do research prior to purchase. You need to take all the rest back and exchange for plants or get a 40 gallon at least. With super filtration (like that for turtles).

They need living plants vegetable matter. If you kept two of smaller size with suitable filter, add some not table salt aquarium salt (like it and need it a bit) and some gravel of suitable size to mouth a bit, and do a small water change each day. They are esp dirty fish (pooh a lot)

Take 1/5 at least of water out a day, with larger end of week, about 1/3 more or less. Keep water sparkling.

Best Sherry

Carp, grow huge several feet and only for ponds.