Brown sludge after UV Steri use

[Bela N]

Has anybody else experience very fine rust-brown particulates forming in their tank after the use of a UV sterilizer? We have a secondary softy/isolation tank that gets less stringent care than our DT. We got an algal bloom & used a 39 W UV stabilizer to clean it up. I was surprised at the amount of fine particulates (I assume the dead bodies of micro-algae) that cover everything. I did a 90% water change to get the majority out. I am trying to use a sponge filter to remove the rest but it cant keep up.

Has anyone had this happen were it affected the corals?

Any comment or suggestions?