I have used NoPoX, and it does a good job reducing or eliminating NO3. I also found it lowered PO4. The problem is, it can work to well. I have weened my tank off of it and it seems to be much more stable.
IMO, your problem is caused by the detritus build up. Nuisance algae does feed off of NO3 and PO4, but it also feeds off of other organics in the tank. Remember, the readings that you get with your test kit are only the items that have made it into the water column. The algae may be consuming other organics in the detritus before it can be converted and make it into the water as NO3 and PO4.
I would work on cleaning up your rocks and sand, and making it free of any detritus. Once that is done, manually remove as much of the algae as you can. Increase your CUC, and try to keep the algae managed. You will always have algae in your tank, you just don't need to see it.
I'll add that I would make a weekly regiment out of blasting any detritus off of your rocks in the future. I do it during my water changes and add a filter sock for a few hours afterwards to catch anything floating in the water.
You should check out threads by
@brandon429, he has an interesting method that would work for your situation.