You shouldn't have to do THAT many water changes. I have ten in my 125, ranging from four to six inches, along with 2 Florida Gars who are about twelve or thirteen inches, and I only do bi-weekly water changes. Nitrates are always under 20. I run a Marineland C-100 and a Rena XP4. If your tank is really overstocked, or your filtration isn't strong enough, you're going to have more problems than nitrates, anyway.