[Delphinus]

Dinoflagellates are perhaps the most nightmarish thing that can happen to your tank. In essence, it's a "red tide". Unfortunately it can be deadly to inhabitants who happen to ingest it, usually snails will drop dead. And it is worse than any cyano bloom because you can remove every last visible piece of it and within 2-3 hours it can look like you removed nothing, due to the fact that dinoflagellates reproduce so fast, a population can double within half an hour or something insane like that.

Save yourself a lot of trouble right now and go immediately to the step of turning your lights off. It is the only method to combat dinoflagellates. If this is indeed what you have, first off my sympathies (many people have suffered this, myself at least twice, others more so). It will hound you and hound you and hound you. Trust me on this one, your only first step to success in battling this is starving them of light. Your big challenge will be to find out how to do this without impacting your light-needing animals such as your corals and clams. As far as I'm concerned, corals can stomach the lack of light for a few days just fine, but clams maybe not. You'll have to figure it out for yourself what's going to work for you, but I cannot overemphasize this enough: you can *only* fight a dinoflagellate bloom by starving them of light. If you have actinics you can try maybe running just actinics for a week, but don't be surprised if this fails - even stray light from an adjacent window may be enough to invalidate your efforts - the only way to fight a bad dinoflagellate bloom is through starving them of what they are looking for.

You can try limiting your nutrient load by reduced feedings and increased skimming and rowaphos and so on, but don't be surprised if it doesn't work. An excess of nutrients may lead to the conditions favourable to a dinoflagellate infestation, but realistically the problem is that they are there, and there is no real mechanism to remove them. Your only hope is through starvation. I'm sorry -- I know you said you only want to tackle a reduced photoperiod as a last resort, but I'm trying to save you a lot of futile effort - they will persist. Your only hope is by removing what they are looking for which in this case is light.

Best of luck. Frankly, your aiptasia and crab problems may seem to add to your headaches, but if you indeed have dinoflagellates they are the least of your worries right now. Get that dinos bloom dealt with, if in the process you can deal with the others, great, but if not -- focus on the dinos first. It can be a hobby killer. I count my two experiences with fighting dinos in my systems as the lowest points of all time with respect to my reef tanks, and believe you me, in ten years in the hobby now I have seen it all, I've seen some nasty things, but very few compare to a bad dinoflagellate infestation.

I wish you the best of luck. Chin up - it can be beat, but you will be severely tested in the meantime.