Should you replace the pump? Yes, replace them.. Replace any piece of equipments in your tank that is giving you issue. Maxijet is pretty cheap. Buy a new one.
As for the UV, why do you run them? Many people don't run them at all. More equipments will give you more issues.
Carbon isn't really needed but it also depends on what type of reef tank you have.. How often you change water? What type of corals are you keeping?
As for me, GFO is absolutely needed to get rid of Phosphate. Try to run a smaller amount and replace them more often. I read online, it is more effective that way.
What type of reef tank do you want to keep? An SPS tank? A softie tank that gear toward having a Mandarin? or a Mixed reef with a Mandarin?
If you absolutely want a Mandarin, then you have to be prepare to keep a dirtier water with a lot of foods in the tank for pods. This will give you a lot of nitrate and phosphate. Big and effective skimmer, a lot of water change, good water flow and maybe Carbon Dosing (Vinegar, Vodka, BioPellet) will keep Nitrate in check. But for phosphate, you still need GFO to control it.
It is much easier to keep a successful reef tank if you know what kind of corals and fishes you want to keep in it.
Also, the return pump you have is really big for your tank and it is loud and add a lot of heat. An Eheim 1260 would be more suitable to your tank. You don't need to feed Phyto for the pods either.. Uneaten food alone will be enough.. Make sure you don't have any food competitor with the mandarin such as a 6 line wrasse
