75 gallon crashing

[mulch123]

Hi every one, I recently upgraded my 30 gallon Bio cube to a 75 gallon with a canister filter and protein skimmer everything was going great until recently my 2 fish got ich. I purchased a product called Ich-X and since using this product my ph, ammonia, and fish have all been crashing my coral beauty angel is almost dead has any one ever experienced this or anything like this.