I have an 8 gallon biocube that I literally do nothing with anymore, and it has 0 nuisance algae. It is skimmerless, currently filter medialess, and gets a waterchange whenever I feel like it, so not often lol. There has been 1 lonely clown for a while and I recently added a clown goby who will eventually be kicked out into the big tank. Also some snails and hermits. Corals are all softies and LPS. I got this tank for free and have made it my "spend as little time and money as possible and see how good it can look" tank lol. The priciest thing I've added is the ATO, which is a must have IMO. So yes, picos can be skimmerless, and I think you will find most picos are. If you seriously want to do a skimmerless pico, I would definitely not strive to follow my methods, I would recommend regular water changes at the very least. I have just been lucky so far lol.