Hydroids-HELP!

[Delphinus]

Couple potential solutions here. Unfortunately there is no real silver bullet.

1. Scrape them off manually.
2. Cover them with epoxy.
3. Blowtorch (no, seriously. It's something I was considering myself)
4. Pressure washer.
5. Used to have them all over the place, One day I noticed I had hardly any in my 75g, but still had them in other tanks. After researching it a little, found that Centropyge angels can sometimes pick at them. I have a potter's angel. That said, I've never noticed her picking at hydroids specifically, but I thought it interesting to note that all of a sudden I didn't have as many in the tank she's in. Could be coincidence, but still noteworthy.

Good luck. In the grand scheme of things there are worse things to get but they're still quite annoying to look at especially when they spread all over the place.