Hi, first off, I apologize if someone has posted a similar problem already. I did search and look and couldn't find anything.

My tank is 20 gallons, pH and ammonia are normal/good ranges, I do weekly water changes (about 30%) and vacuum the rocks when I do the changes. My goldfish is about 7 years old and lives with a pleco, who I have had for about a year. I feed my goldfish flakes and peas.

My problem is, as of late my goldfish has had these twitches in his fins, and today I noticed these really tiny bubbles stuck on him, in various places, some in these odd strings of bubbles. They are bubbles, not eggs (my fish has had ich before so I know what that looks like, and this isn't the same).

I am thinking its some sort of parasite problem but I really don't know. Fish has lost a lot of scales over the past few weeks (could be the pleco from what I've read, although I've never seen it do anything aggressive to the goldfish). Goldfish tries to scrape his scales on the rocks at the bottom of the tank. So it may be that he is losing scales that way. I don't know.

I've put some salt in the tank based on the recommended dosage. And I've been using Melafix. Filter is Penguin Biowheel 160 model for up to 30gallon tank and I set it up two weeks ago.

If you can deduce what my problem is based on what I have provided...I appreciate any feedback!

With fact your fish is rubbing itself against objects in the tank probability is a parasite infection. Do you have an airstone in your tank? Do the bbbles disappear or they permanent. If they disappear and you have airstone then your Goldie likes to play in the bubbles and sometimes bubbles stick to your fish.

That was my line of thought, too.

There is an airstone (one of those long skinny ones that make a lot of bubbles). And yes, the fish does like to go near/in the bubbles. I guess they might also be from the filtration system which makes lots of tiny bubbles.

I read somewhere that bubbles on the fish are painful, and that is why I was concerned. The bubbles do fall off.

So it sounds like they may not be related to the missing scales/twitching.

Just wondering about a few things -

'I've put some salt in the tank based on the recommended dosage. And I've been using Melafix. Filter is Penguin Biowheel 160 model for up to 30gallon tank and I set it up two weeks ago.'

- is this set-up new or just the filter?
Also, when you say normal levels for ammonia and nitrite, can you tell us exactly what the readings are in numbers? There should be a zero reading for both. Especially important to know is the exact PH of the tank (and also the tap water for comparison).
I agree with Blue that if the fish is scratching on the rocks it indicates parasites. But in addition, the plec could be attacking the goldy at night and losing him scales that way. How big is the plec? They get a taste for the slimecoat once they grow bigger and, as you've read, are not recommended as tankmates for gfish. Does it look as if there are strands of slime to which small bubbles might be attaching? Can you check his mouth for any fluff or cotton strand, too? Lift him just above the water line and look into his mouth as he gapes?
It would help if you could tell us a little more and post your water results. It would be good to make a diagnosis soon.