I'm pretty sure that is not Ich. I believe that it is some sort of fungal infection.
My guess is that the fungal infection is because your tank is overstocked. I would recommend that you do a water change and buy a liquid test kit to test nitrates, nitrites and ammonia.
Knowing your water parameters is key to maintaining a healthy tank, especially is the tank is newer.
Goldfish are huge waste producers and keeping multiple goldfish in such a small tank means that your water goes bad really quickly.
The pleco may have carried the infection, but I'm guessing that the immune systems of the goldfish were already comprised. How long have you had the goldfish?
I think your fish have Cotton Wool Disease and from what reading I did on the Internet it can be easily treated.
I would recommend that you do a water change to help with the quality of the tank water.
You could use any number of methods to treat it...Malachite Green, Jungle fungus Eliminator(US) or Anti-Fungus-Remedy(UK) or aquarium salt baths.
**I have never treated Cotton Wool Disease or used any of these products to treat a fungal infection so my knowledge of them is limited.**
Anyone else have any ideas??
