I found a small air stone skimmer on ebay from China for $20 to replace my JBJ skimmer and the tube diameter was only 1.5". It worked great.If any one has suggestions for a skimmer that would work with 2.5 x 2.5 feel free to post it
https://www.ebay.com/itm/Protein-Sk...296551?hash=item287321f2e7:g:u2kAAOSw2pBcLFQh