Most likely the problem was with the skimmer not working. You took out a lot of material. That may be all you need to do.
However, to answer your specific question, I prefer an iron based product, such as ROWAphos. It can be simple placed in the sump, where water can pass through it. Best results are obtained by using a "reactor", in other words a filter that forces water through the material.
When you use such a reactor, you want the flow to be moderate. You need to give the material time to do it's job. You can usually simply plumb the reactor using a T and valves to connect it to the main return line. You can also use another small pump, but there is really no need.
I'm not a fan of UV, but I don't think it would have any effect on Chaeto being grown in the sump. More likely would be the lower quality of water, due to the skimmer not working. Lighting could also be a factor.
|