LyndaB said:
Are these tanks cycled?
Did you check for illness in the tanks at the lfs?
Is there a reason you don't quarantine?
How did you acclimate the fish?
Personally, I think there's no reason that ich should ever get this bad. If you monitor your tanks carefully, as you should whether or not you have new fish, you should be able to catch ich at the very beginning.
I don't use meds to treat ich. I raise the heat to 86 slowly, add an airstone to provide additional oxygenation, and gravel vac every 2-3 days.
Usually, if your water params are healthy and you keep your tank clean, you won't get ich.
Ick is almost in every tank and on this case your just not lucky as it comes from a store!!
Ick is stress related, bad water condition related but mainly temperature related.
So even you you do everything right if there is a temperature drop or boost for 2 F and more, there is a chance of ick.
If you let you home temp goes down at night that could happen to everyone using bi-metallic heater. (99% of heater on fish market are bi-metallic)
The temperature treatment is good, if it does'nt work here is a little med:
To treat it easy, you can use formaldehyde, 37% at a drug store and use 1 drop per 2 gal day one and 2. Third day change 40-50% of the water amd do a gravel vacuum. Do it again until symptom disappear.
You can do better, by adding the recommend dose of formaldehyde in a test tube, add 1/4 the recommended dose of malachite green and the 1/4 recommended dose of methylene blue in the tube, mix well and put it in the water. Its called FMC and its great against ick.
For sure when using malachite green never let the light open as it stop the effect.
Warning:
1-FMC and formaldehyde are strong, dont put more than i said its enough.
2- dont use with temp of 28C and more.
3- scaleless fish, tetra, catfish : use 2 drop per 5 gal. of formaldehyde. Same blue and green.
4- formaldehyde is hard on plastick so use glass test tube or do it fast(3 min max in the tube).
Formaldehyde, blue and green are cheap and useful together!!
Google FMC you will find how to make it!
Formaldehyde is very volatile.
Good luck