Doesn't sound like you have a very heavy bioload. Are you seeing any adverse effects from high nitrates? Id probably just stay doing 10-20% water changes weekly and try to get some more cheato in that fuge. That's how I got my nitrates under control when I had nitrates as high as yours, got mine down to 10-20 in a couple months following that. I'll add that I use a couple cheap led grow light bulbs from ebay on my fuge and grow cheato like crazy.
Good luck
Do this^.
I did the same to get phos and nitrates lower. I bought a Fiet grow bulb at Home Depot and a clip on lamp for around $20. You can get that going if you are strapped for cash for a better light.