I personally like IO, and reef crystals are the only alternative that I would consider(same product, with more trace elements)
James, one question, did you actually test your system for phosphates?
true it may be in some salts, and some salts have also discovered they are there ,and some of those have even taken measures to eliminate them. I would reccomend testing to see. If so, then work on lowering them.
If NOT, then take a look at all your parameters and circulation. It could also merely be from having such a young tank. Both are common in young aquariums, very common. In fact, diatoms are part of the maturing cycle, JMO.