Innovative Marine skimmers work very well and have much larger cup than the 115. Reef Octopus makes 2 nano skimmers NS-80 is only $43 has Italian pin wheel pump and a drain tube on the cup. It also has rotating tube to set water height, easiest of all to tune. i was very impressed for the price. I have also tried the BH-50 little hard to adjust and larger but also works well on my 27G SPS tank. Last one I tried was the Eshopps nano, held on by magnet check if it will fit, great skim (like tar) and decent size cup are pluses here.
#1 innovative marine
#2 Eshopps - works best
#3 for smaller tanks the $43 NS-80 is the one you want. It would be #1 if I could handle bigger tanks