Saltwaterman, it looks as though you have only posted your nitrIte readings, but I don't see the nitrAte readings from reading the thread. (I'll apologize now if I missed it.) As stated previously you ought to check both nitrAtes and phosphates when you're facing a nuisance algae outbreak. (NitrItes and ammonia should both be zero all the time in a cycled tank.) You want to target less than 5ppm for nitrAtes and 0 for phosphates. If your filters on your RO
are very old, they might be letting nitrates or phophates through whenever you top up or do water changes. The way to check this is with a TDS
meter checking your RO
water before you add salt. If it's not zero, that could be your problem. If you are gettgin a zero, water changes and phsical removal do help to starve and remove the stuff.
Also, the algae can bind up either one to show a zero reading on either or both kits. In other words, the algae actually absorbs the stuff before you can read it in the water column. Consider adding a phosphate absorbing media to your filter if possible. (I've used a pad in the past myself. It did make my skimmer NUTS for a day.)