Dont decorus get like 8-10"? In my tank I have 2 multi around 3.5" a flavitaeniatus at about the same size two Valentini(hybrid) one 3 one 4 and a golden nigrita at about 6" and a bristle nose pleco. 3 delhezi, 2 gold dust, long fin sen, polli, albino sen, Palmas, moke, and 11 ropefish. Cats are fine dont bother the polys and polys dont bother the cats. Now I wouldnt put those cats with large ujs or any ljs. As these are some of the smaller synos not the smallest, but of the ones readily available some of the smaller. I lost a cat to one of the teugs before they got rehomed. Teugs were 17+". Id say del and down in size will be ok. Biggest del is 13-14". Of the polys listed the dels will get the biggest but at most 14".