Folks, if you've recently upgraded or renewed your annual club membership but it's still not active, please reach out to the BOD or a moderator. The PayPal system has a slight bug which it doesn't allow it to activate the account on it's own.
The only thing I would say when it comes to dealing with NSW, would be that as hobbyists , we should take the extra step of acclimating any new fish and corals to a NSW set up.
Assuming that we're not getting them directly from the ocean, I feel that ready made sea water may be too "pure"...
Check the venturi on the skimmer and make sure that it's all the way in place. It's possible that it may be loose and forcing air bubble out through the gap. Also whilst you are at it, make sure the venturi isn't cracked. The picture is just for reference
You really can't blame the Blenny though. if it was just tossed into the tank without researching to see if it was compatible with horses, then things like this are bound to happen.
Is the blenny actually attacking the seahorses? I've never known them to aggressive towards other fish.
The membranes will fit, but depending on your unit, the option may be to replace the cartridge. I had a generic unit a while back that allowed me to to replace the cartridges.
Like mentioned, maybe do a series of water changes then set up another ICP test to see what happens.