Those rocks with algae on it is commonly used in refugiums. Buy those without algae or tonga branches. And you would need STRONG lighting for marine tanks if you want to keep corals
1)Its probably a flatworm so KILL IT
2)Thats probably some sort of worm or stuff that builds a tube using all kinds of shit. Dun need to bother.
3)Ya. Thats a doing of a crab
i got a cuke and a brain from them last yesterday. the guy there very friendly and would tell advice you on how to keep and stuff. he also tols me next week got stock