The issues with the seastar have nothing to do with the phosphate levels (unless they get REALLY high), think more along the lines of what folks have posted in terms of acclimitization or changes in salinity in general.
How do you replace your evaporative losses in the system? This alone may be a telling feature of your system, and unless automated in such a manner that it prevents wide swings in salinity, can be a major cause of
Asteriod specimen loss in home aquaria. The issues associated with acclimitization may occur prior to your acquisitiion of your seastar, so there may be nothing you can do at this point, but maintaining a consistant steady salinity is a must for these beautiful echinoderms to survive in closed systems. Thick-bodied
Asteroides seastars like
Fromia and
Linckia spp are very susceptible to changes in salinity. They have evolved in salinity-stable environments and unfortunately, may succumb to unstable environmental change by rupturing their hydrovascular locomotion system, resulting in death of the specimen involved, see
THIS THREAD for more info on the
Asteroides seastars and their problems with shifting salinity.
As far as how to use the Phosphate reactors, placing about a
level measuring tsp of rowawphos (4.2ml) per USG is the recommended dose (250ml GFH per 250 liers total system water), however, I personally drop the dose to a tsp per 5 gal for maintenance with a once every 30 days change of medium, and if you have either new lights or think these may be an issue with photoacclimitization (new specimens, sick acro, etc.), even a remote one, drop the dose to a teaspoon per 10 gal and change it once a week until you see either a drop in
nuisance algae or your measurable free phosphate in the water column drops to zero measurable levels. If you have measurable levels of phosphate, it is more likely worse than what you're seeing through the test kits. This is not to say that the actual value of phosphates will be zero, but the drop in nuisance algae should be a good key for your dosing. Using these low doses and changing more often will prevent issues with stony
Acroporids and reported tip bleaching, in spite of the fact that it will take longer to drop the phosphates. I would rather deal with siphoning out algae or other growths than deal with bleaching my stonies any day.
HTH
