A bristle tooth tang would be a perfect addition to the tank.  Not sure your tank is mature enough to keep chaeto alive and actively growing.  Try to find a clean source of different coraline algaes.   
 
J@L sells Tiger Pods.  If you can find someone with a perfectly clean tank with no bad things in it add a piece of live rock from that tank.  Not sure where you are going to find that.   
 
My small tank is pretty clean although it would be a source of cyno, diatoms, hair algae and dynos even though they are currently not visible I have had them in the past few years so they are only actively waiting for poor conditions to return to encourage their growth. 
 
Not a big fan of hermit crabs.  Water changes, water movement and a good skimmer is about all you can do.  Check your source of fresh water as well, change filters add a DI Filter if you do not already have one. 
		
	
		
		
		
		
		
	
		
		
	
	
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