slow motion tank set up.

tom reilly · Apr 26, 2016

Ok. Back with another question.the tank I'm conversion to salt's a 125 gal.
I bought it used at least 6 years ago ,stripped and resealed it. Currently has a eshopps overflow with two 1 inch tubes.
I would like to drill this tank for internal overflows. Is there any way to tell if the glass is tempered or not?
Thanks in advance.

sbash · Apr 26, 2016

I just went through this situation. After a bunch of research and testing my results were inconclusive. The only way I have ever been able to tell if the glass is actually tempered or not is to simply start drilling. Unfortunately, that is not an acceptable answer.

The best test I found (not that it worked for me on my tempered tanks) was to use a computer/tablet screen and some polarized 3d glasses. Hold the screen inside the tank, and look through the glass (while wearing the glasses) at the screen. There are several YouTube videos about such tests.

That said, one of main reasons the glass is tempered is so the manufactures can use thinner glass. For example, my 65 gallon has 3/8" thick glass, and is not tempered, my 55 gallon has 1/4" glass and is tempered. My 220 gallon (not tempered) has 5/8" thick glass, while other 220 gallons I have seen have less than 1/2" thick glass. With this information, you can likely deduce whether it is tempered or not. However, the risk is still there that it is tempered.

If you are drilling the end of the tank and it breaks, the cost would be fairly low to replace that pane of glass. I know, not super helpful, I post this more to provide empathy, as this is a brutal dilemma for everyone who ever wants to drill a tank...

CodyRVA · Apr 26, 2016

You can test accurately every time with a cell phone and polarized sun glasses. Place the phone, lap top, tablet, etc inside the tank facing outwards. Easiest to test when the screen is white, usually your default browser window works. While holding the glasses, look through them and rotate them. If you see streaks of dark/gray color it's tempered and can not be drilled. If you see no streaks and only a change in lightness to darkness, its non tempered and can be drilled.