Hey Jeff,
Hang in there... everything in this hobby takes an incredible amount of patience, and if you want to get good, lots of time to research. I did want to state a few things that may put your mind at ease and maybe give you a few steps to take moving forward.
First, if your tank is only 6 months, it is still very young and can go through cycles of uglies. Cyano outbreak you had, is proof. That being said, I think you should let the tank do its thing and mature some more. Your maintenance schedule seems right (the once a week one). Go back to that and let the tank settle in. Increase some flow if you can and leave the sandbed alone for now. Occasionally stir it up a bit, but not too much.
Second, tanks dont like change. Make small changes and fiddle with it as little as possible. You'll be surprised how much better things do. Obviously keep up with your dosing, RO top off, water changes, and algae cleaning. But otherwise let it do its thing.
Third, let nature clean the tank. Stock a lot of CUC (Clean up Crew), overstock it for now with those that will eat the GHA. They'll put a dent into it a lot better than you can ever do.
Fourth, although you are reading acceptable levels of Nitrate, thats because the GHA is absorbing a lot of it. If the GHA was gone, you would likely see a much higher level of that. So you likely have a nutrient problem. Most likely culprit is overfeeding. Try and reduce the feeding a bit, and if you are feeding any coral food, dont.
Fifth, check for Phosphates. That could be a major culprit in nuisance algae too. GFO and a little carbon can help you there.
Sixth, look into a bacterial culture boost. It seems to me its possible that while doing frequent water changes to get rid of Cyano, you may have destabilized the nitrifiying bacteria cultures. In the alternative, you can ask for a small cup of sand from a well established tank (that you trust to be pest and disease free) and put that in your tank, to help seed it with more types of bacteria. Then do your normal weekly upkeep and let the culture establish. You're basically doing a new cycle, potentially when you did too many water changes.
Finally, and this is a completely personal opinion, so take it for what its worth. I dont like Chemi Pure. Anytime I would use it in any of my tanks, it always made coral and inverts react oddly to it. It has a tendency to strip things fast and then not do too much after. Go into the chem section of this forum and read up about what Randy has to say about how accurate the company's claims may be. Instead, get two separate media baggies and run GFO (my fave is RowaPhos) and some good quality carbon in separate bags. Then you can change each of the media as needed and have much better control.
Sorry for the long *** post, but I hope any of this will be useful to you.
It’s weird how two reefs can be so different
