Keeping da tank clean (need help)

So I have the Rena Filstar xp3. I have been told by few that it's all I need running to keep my 25-30 gal tank clean. Is this true?

When it comes to keeping your tank clean reliably, the only way is clean it yourself. A magfloat n a syphon hose are your best friend. A couple turbo snails do wonders in a reef tank

My question was having this Rena Filstar xp3 can I get away without having a skimmer

They perform completely different functions. So no, it will not replace or remove the need for a protein skimmer.

The Rena filter will give you mechanical filtration and an area for chemical filtration (AKA, running a carbon pad) but will not remove proteins that a protein skimmer will remove. No form or size of mechanical filtration can replace a skimmer.

That said... a low bio load, frequent partial water changes, a large refugium plus excellent mechanical and chemical filtration can reduce the need for a skimmer low enough that one isn't necessary... especially in systems without SPS corals, clams or anemones.

So what other system do I need if I dont want to spend the money on a protein skimmer? Can you give me more info on what these are? (a large refugium plus excellent mechanical and chemical filtration) How good is the Rena Filstar xp3?

I ran twp rena xp4's on a 240 freshwater tank for a long time. Imo rena canisters are excellent. But having said that i never used one with saltwater.

My friend got the tank it was being used on. Which was a saltwater tank. They had a proteint skimmer on the tank as well but said they never used the skimmer. So that where all of my questions are coming from. This tank I have the xp3 on is only 30 gals. Over kill bad good. The tank it came off of was a 55 gal.

I ran a successful skimmer less 29g for a long time. I kept my bio load at three small fish and kept a large clean up crew full of many different snails, crabs and scavengers. I also had a live rock rubble area that was full of rock rubble that had the most feather dusters and pineapple sponges and pods I've ever seen.

For mechanical filtration I just kept filter floss at the top of my media rack. I had purigen and chemipure elite as chemical filtration (sometimes in my media rack, sometimes in a homemade reactor, sometimes in a next reef shorty reactor).

I did a 5 gallon water change every Monday night and a 10g once a month. I also underfed in my opinion on purpose. All this reduced the need for a skimmer tothe point that I felt confident without one. It was all very intentional however. It was built off months of study, wise advise and strict habits. Skimmers make mistakes in a reef a bit less likely. I'd suggest them for a typical new hobbyist. I however also discourage becoming a typical new reef hobbyist (aka, over feed, no water changes, over stock, under filter and under light). Haha.

You're taking the right steps asking questions now. Keep it up. :-)