I second mike here,
A quick big drop in po4 can sock coral and paired with spik in salinity and alk can magnify the effect.
Although I would be suprised if the al99 stripped the po4 so fast. If it was rowaphos, double the recomended quantity would zero po4 in matter of days. But al99 is much slower in action.
But you should test po4 for sure, if it's too low, reduce the flow on the al99, depend on how low po4, reduce the flow accordingly.
A quick big drop in po4 can sock coral and paired with spik in salinity and alk can magnify the effect.
Although I would be suprised if the al99 stripped the po4 so fast. If it was rowaphos, double the recomended quantity would zero po4 in matter of days. But al99 is much slower in action.
But you should test po4 for sure, if it's too low, reduce the flow on the al99, depend on how low po4, reduce the flow accordingly.