I'm having some issues with 2 of my hippo tangs. I have had them for a few weeks and they all have been active. I was away from the tank the last 2 days and today I found that 2 of my hippos have went into hiding. They are not that active like the other 2 are. There are no signs of aggression towards any fish in the tank. One of the hipos is hiding in the shade with its fins fully extended. The other is hanging out under a coral. The one hanging out under the coral is breathing extremely fast also. Any ideas what is wrong with them? I'm also trying Voogle by Easy Life to see if this stuff really works or not.