algae control

[hypoxia]

I'm dealing with a hair algae outbreak and I've noticed that one of my zoa frag plugs is continually overgrowing with algae. The zoas have grown much more slowly on this plug than any other (which is a pity because they are flaming yellow, orange, and green) and the algae will eventually choke them off. I'm preparing a small chunk of rubble to accept the zoas when I remove them from the plug with a razor blade.

So my question (finally!) to y'all is: do some plugs have a chemical composition that encourages algae growth somehow? Brands to avoid?

[Redwinger]

Well IME the aragonite ones seem to never do well with frags on them and also seem to grow algae pretty well. I believe there are some phosphates locked up in the aragonite that is causing it.

[hypoxia]

This plug does seem to have a different texture than the others. It's rougher, more concrete-y.