haha, well since I still have them I might be the wrong person to ask. In my case they're not crazy out of control, and I've only ever seen them physically on one coral that I don't really care that much about and they haven't seemed to be impacting anything except how the tank looks (i.e., they're not slowing down the growth of anything, even the one coral they sometimes seem to 'dust'). They wax and wane for no apparent reason as far as I can tell, and sometimes my sand turns brown, and sometimes I can only notice them around the perimeter of my rocks. As a result, I've decided to just live with them because if you do searches online, the kinds of interventions people do to try to completely get rid of them are pretty extreme.
Some of the things people suggest:
1. a complete lights out (as in you cover your entire tank in a blanket so that zero light gets in) for anywhere from 3 to 10 days depending on who you ask.
2. Drastically reduced photoperiods after that
3. Dosing the tank with varying amounts of hydrogen peroxide
4. Raising the pH above 8.4
5. massive water changes
There's an article on advanced aquarist here:
http://www.advancedaquarist.com/blog...sons-i-learned where the guy says you basically need to do all of that together to beat them, along with getting your tank's nutrients way down to the super low range and physically removing as many of them as possible, both with a filter sock and via siphon.
There's also a biocide/algicide from Fauna Marin called Ultra Algae X that claims to directly kill dinos along with all sorts of other kinds of algae, but it's instructions are pretty specific and also involve some pretty restrictive things like reduced photoperiods and such.
Since my problem isn't *that* bad, to me the "cures" sound worse than the disease for their potential to throw something else out of whack and I've been content to just live with them as I'm really the only one who notices them. I have definitely noticed a correlation (which may just be an accident and not causative) between how often I change my filter socks and how brown my sand gets as the day goes on. It's just speculative, but I've looked at mine under a microscope and those stringy strands are actually made up of some highly motile little dudes. I think at night they disassociate and enter the water column to some degree, which is why it seems better in the morning. Theoretically a small enough micron filter sock might help.
Heres a couple pics of a 'strand' the a clipped out of my tank under the scope (I have a terrible scope camera so the picture quality is pretty bad):
And a short video of them in motion. The 'strand' literally disintegrated into a mass of this:
If you find a solution that doesn't involve injecting my tank with highly reactive chemicals, messing with the pH, dosing it with some unknown poison, or stripping the water of nutrients to the point where my corals stop growing, please, let me know.