Those blood sucking isopods are still fresh in my memory from ten-twelve years ago when I had a tank with real live rock. I would hunt them down every night for weeks. Awful pests.Aiptasia are barely a problem nowadays, you only ever hear about people putting in work or predators to get rid of them, never really about people restarting their tank or giving up entirely because of them anymore.
All the things you listed just vary in how annoying it is to deal with them, but you can deal with them, so they hardly qualify as the worst.
I'd say a good contender are fish attacking blood sucking isopods, nothing you can really do besides going fallow for a year or more, trying to catch them every night basically forever, or restarting the tank
Maybe coral diseases leading to stunted growth forever
Unlikely but not impossible, I have a fairy wrasse that eats algae with my tangs out of the clip, I wouldn't say it's the norm.I literally saw one creep onto a healthy polyp and chow down, pulling it off took relative force.
Flatworm exit works nice might half to do it once or twice. Add a good air stone in the system. I added Christmas wrasse and sixline also worked greatCurrently dealing with rust brown planaria/flatworms. They are ugly and a nuisance more than anything. I keep on top of them with siphoning. I bought a springer's damsel to try natural control, as suggested to me by the shop owner, but it shows zero interest. Next step will be flatworm exit, I guess... Though I'm reluctant to try it.
This is a challenge. Have you attempted removing a rock and allowing the sponge to experience air contact? That with a hydrogen peroxide exposure might work to control and remove this?The worst pest for me has been this red encrusting sponge. It is taking over my tank. Every sps is turning white at the tips. The tips turn pink shortly after, which I assume is the sponge growing on the exposed skeleton. ICP test shows everything acceptable. Assuming the sponge is releasing some type of toxin. Recently changed carbon and have been running a poly filter. Nothing has helped as I watch my reef slowly get destroyed