I used to have a 25 gallon tank for softies only without the sump, running with 2 cheap 402 Aquaclear powerheads and a Eheim Magnum Deluxe filter. Water change every 6 weeks without using any skimmers, I actually even didn't know a reef tank needs a skimmer
but that tank was lasted for well over 4 years before I shut it down to get a bigger tank.