Crox,
Welcome follow Brooklyn'er!
I am by no means an expert, just an avid reader, so I am going to pass on somethings I have read.
You may have added too many fish at once. Too many, too fast will stress them, making them vulnerable to ich. Kindof like stuffing 30 people in an apartment meant for four people and never letting them out! Immune system will drop and if one person is sick, everyone will get sick. If you have another tank try to separate/QT them.
You will, very likely, need to QT your fish, otherwise your fish may pass the parasite around to each other like a bad cold in an office. For more information look at the top of this forum for QT/hospital tank setup. This is a possibility even if they heal and shake off the ich themselves.
You can set up a QT pretty fast and with not that much cost. Get a long clean rubbermaid [$10], a power filter [$20] and a heater [$20], to start. You should also provide some hiding places with PVC pipes in the tank. Don't add any LR or Sand. You can use this everytime you add a new fish, just to make sure it is clean and healthy.
After this is done, I think, you should go the hyposalinity route. Considering the number of fish you have.
There is probably a lot more that I am forgetting but the experts will likely see this soon and respond as well.
Good luck!
E
