Argh, take note, why water features suck

[Lija]

It reads anything, but on a surface.

oh I lied.... Pardon me, forgot, I have a few glass thermometers the floating kind. Paul said these are the best for anything.
i believe 2$ at Walmart. These would totally work for betta or frog tank

[Mentat]

A Floating thermometer like Lija mentioned is best deal for Betta. Sorry for water leak ; but that is nature of silicone when used to build a "glass wall dam" in an aquarium/enclosure. The issue is, new silicone wont stick well to old silicone or if any glass surface has a contaminant on it.

For it not to leak you have to scrape off all old silicone so that none comes into contact with new one. Also, after scrapping it; a cleaning with acetone (wear gloves and eye/breathing protection) to remove any contaminants and silicone remains is required .