How to tell if you're overskimming?

[Slick Fork]

Hi there,

I was wondering at what point do you start overskimming and how do you tell? I'm currently running a vertex in-180 that I had bought for my 150 gallon (total volume) system on a system that's running roughly a third of that at about 55 gallons total volume.

My coral plans are probably going to be more on the lps/acan/zoanthids, etc. With only a couple of sps.

Any thoughts?