75 gallon 20 months old

[Galvan]

I have a 75 gallon tank with 90lbs of LR about a 3.5 inch sand base with sump and skimmer. 8 animals and 3 corals. I'm working on getting my Nitrate down it is running about 80-100ppm and has always been this way, i just have not been able to get in the 0-10 range. Question is can I do 10 gallon water changes every week in order to try and get this down to about 5ppm. I'm afraid if i do too many water changes this may some how affect my fish. Is too many water changes bad