sorry for your loss bro, water change not likely can help for parasites issues, unless ur tank has alot ammonia and its causing more stress to the fish. 1st thing to do is to correctly diagnose it is ich or other parasites like velvet before u can start treatment. You can google for pics to differentiate. There are few “proven” methods on the google u can look out for. 2nd question is whether your tank is reef or Fowler. Some common methods i can think of which help combat or eliminate ich 1. Copper 2. Tank transfer method 3. Hypo-salinity 4. polyplab medic 5. UV 6. Enrich food 7. other medications like formalin. If your tank is reef tank, method 1,3,7 does not apply as u cannot do that to reef tank as will kill corals and inverts. You will probably need a dedicated QT tank to administer treatment. My own experience is using QT tank and administer copper to treat and it does works. But dosage need to be careful and QT tank water quality can degrade fast if not cycled properly. For TTM (tank transfer method) also need 2 tanks to do constant transfer of fish to break the lifecycle of ich. If your tank is reef tank and u dont have QT, u can try method 4,5,6. method 4 is using H2O2 (i tink) to kill the free floating ich parasites. alot local reefers had used and reported success but i didnt use before so cant comment too much. Method 5 also will work but u need spend $$ and get a good sized UV. For UV to work need to have precise flow rate vs wattage so u can kill the parasites effectively. But this can be costly as large UV is EX. The reason why u need large UV is u need higher contact time for UV to kill the parasites at a decent flow rate. u can opt for low flow rate but it wont be effective as u need to turn over the tank volume fast to kill the ich. Method 6 is easy, just feed more nutritious food like frozen mysis and enrich with selcon, u can add garlic to entice fish also. Some say garlic works but i tried it doesnt work for ich, at most is make the fish appetite better bah. With fish eating and less stress the natural slime coat will be better and more resistant to ich. This is a huge topic by itself, u can do more reading up. I am by no means expert and above is just based on my own readings and learnings and maybe not 100% correct also so other seniors reefers can chime in. Hope got help u. Sent from Singapore Reef Club mobile app