My fish are dying rapidly. What can I do?

I started scraping walls of tank and removed 10gal water. Nothing was added and gobie died within 2hrs. Purple tang is on the bottom barely alive. Some said it may be fungus. I don't have a treatment at home but I did a 60% water change with RODI water. MY erfly fish is in distress and breathing rapid and laying on the ground a lot. The clownfish still seems ok. Please give me any suggestions or possibilities of what can be happening.