Ok, here is my standard post for SW PO4
1. Do they use RO
water? If not your should make the switch and work on doing some water changes. If you already use RO
water, test your source water. You may need to add a deionizer to it, that is the stage that removes PO4
. This is the most important step.
2. Review their feeding habit. Are they overfeeding? Do the fish eat what you put in at feeding time within a few minutes, or is there food lying around the bottom after? Also, if you use frozen, make sure to drain the as much of the packing juice as you can before adding.
3.Do they have a skimmer? If so, is it producing daily amount of dark thick "skimmage'? Adding or upgrading a skimmer may help.
They can also run a PO4
sponge which will help, but they need to address the other underlying causes.