no thats not to much at all alot of people on here (including myself once my 120 is set back up) do 50% waterchanges weekly as long as the water your putting back in is same temp so it doesnt stress fish then its good that you do big waterchanges, i would actually do like 20g wc if i were you just to make sure the water stays really good (right now since i have delicate fry in a 20L tank that i feed multiple times a day, im actually doing like 8-10g changes every other day)