Need Help lowering nitrate levels


Reefing newb
Hi my name is Rebecca and I have never tried forums before so forgive me if I do something wrong. I am pretty desperate to lower the nitrate level in my 55 gal reef tank. I have not been able to buy any corals or anything else in quite some time in fear they wont tolerate my aquarium. So this is a quick idea of my set up. I have a 75 gal hanging filter, a fluval G3 floor pump filter, a aqua max protein skimmer, a uv sterilizer, and 2 e wave pumps. I also have about 35lbs of live rock, a few mandros plants and 2 shaving brush plants. I also used live sand when starting out my aquarium and I have a reverse osmosis system for water changes. Now I have spoken to a few people at various pet shops about how to lower my nitrate and have had little success. I clean my tank 2 times a month changing one third of the water and I use a siphon to get as much waste as I can but when I test my nitrate level right after cleaning my levels are still high. I don't know what else to do. Thankfully none of my fish or corals have died because of this but I know it must be stressful on them if anyone has any suggestions please let me know I would be very grateful and if you need more info just ask. Thank you
How long has your tank been running? Do you ever blast your rockscape with extra flow to remove detritis? How often do you deep clean your filters? Hopefully by now you have fixed your problem but thought these may be things for you to look at. Happy reefing :D
A few things come to mind .....

Canister type filters need to be throughly cleaned weekly if not every other day .
They trap nitrates .

Have you tested water quality before mixing ?

So here is a little food for thought .

If your new water is 0ppm nitrate .and you do 50% water change.
The best you will get is 50% of the existing level.

Larger water changes is key .

You could try carbon dosing .
Nopox is amazing .