First water change?

My 90 gallon tank is finally cycled and I added 5 green chromis and a pecula clownfish

When should I do my first water change?

 

Should have done one right after your cycle had finished. Do one this weekend.

 

ok cool

 

+1 to above

Since the cycle is complete what are your parameters?

 

Is 15-20% change good? Or should I do more?

 

15-20 is fine.

 

This is one of the reasons I asked you to post your parameters. I’d err on the side of caution and do a 20% water change (ro/di of course). Followed by 10% weekly Changes and close monitoring of conditions. Once your tank is established you can slack off a tad on the testing – but always attempt to stick to a scheduled maintenance.