Bubble magus recommendation is far off
I have had to raise my Curve 7 so it is in 6in rather than the specified 9in for it to run properly.
Have a search on google and you will find the recommended depth is way off in many real life applications
https://premiumaquatics.com/products/simplicity-120dc-protein-skimmer-brand-return.html. Look into Simplicity 120 skimmer, I know I have mine in 7" of water, they are on sale at this site great skimmers great C/S 3 year warranty and they answer the phone and answer questions and get a product right out to you. I did a small search and it is tough finding a skimmer fo 6". usually skimmers that go in shallow water have powerful pumps, kinda of hard when you have a small tank.
The Aquamaxx nf-1 would work, its a beast of a skimmer for how small it is. Also fits in the back of most AiO tanks, I have one on my 28g Nanocube, and it’s quite, no micro bubbles and pulls out a ton of skimmate. Aquamaxx skimmers, in general, are well made and user friendly.