I've used it a few week ago, for two consequent days. I've had three clams at that time: 6" derasa, 6" maxima and 2" crocia. So far, I didn't notice any changes in behavior or growth.
I could not measure any phosphate during and after treatment. There was a minor spike in nitrates, but still ten times less then maximum acceptable range for reef tanks (sorry, I don't remember the numbers). I did pull out as much slime as I could before treatment.
So, I would say, the RedSlime itself does not affect clams directly.
Simonh,
RedSlime is beleived to be an antibiotic.