I fear you are onto something. I've never dealt with this.
GAC?
I did use activated carbon and even a little GFO (changed every 24 hours for anti-silicates – not left in for anti-PO4) during my bloom just in case it would help, but I honestly never researched if carbon really could help or not.
I think cleanup crew death is from exposure due to eating, not from exposure in the water. But from some related reading, it's possible these toxins can also have an inhibiting effect on autotrophic plankton...sometimes even a lysing effect. So I could be half-wrong and there could be some indirect effects on the animals too. (It's a brilliant survival capability...what better way, as the starving dinoflagellate, to solve your lack of dissolved nutrients!)
So IMO, using a small amount of activated carbon that gets changed frequently is not a bad idea at all.
If you do, I recommend to use manufacturer guidelines for quantity and replacement....go on the lower end of quantity and replacement interval if they give a range.
Once I had signs that the toxic phase was done I quit using activated carbon (and GFO) and have been fine.
Even with that, my first replacement clean up crew was too soon and did not make it. Coulda been a bad batch of snails, but I assume it was still toxins in the algae. The second batch I added a week or two later did OK and is still with me.
Now to hear back from
@peasout05! Hopefully things have turned around!
