Drilling and adding overflow

[JMM744]

I have a 70 that was set up for a syphon overflow on the back as well over the top return. 120 has duel overflows on the back wall and drains out the bottom with the returns using two of the bulkheads in the bottom and coming up the inside of the overflows. I would like to drill both tanks through the back and either use a coast to coast or a ghost overflow on them These tanks are bare bottom and I am contemplating bringing the return on the 120 back through the bottom and keeping the return water close to the bottom to keep the sediment on the tank floor in motion using the flow. The 70 my thought is to drill closer to the bottom on the back wall and do the same with the return flow. Having never done this before I am much interested in any thoughts, warnings or experiences in doing this.
Thank you,
Jim

 

[ndrwater]

Most tanks are easy enough to drill. Tons of YouTube videos covering the matter. Big word of caution though, MANY tank manufacturers used tempered glass for the bottoms. Tempered glass is NOT drillable. Tempered glass will shatter when attempting to drill.
Easiest way to determine this (although not foolproof) is to look at the glass through polarized sunglasses. Tempered glass looks to have an oily film through polarized glasses. Regular glass does not.

 

[JMM744]

Most tanks are easy enough to drill. Tons of YouTube videos covering the matter. Big word of caution though, MANY tank manufacturers used tempered glass for the bottoms. Tempered glass is NOT drillable. Tempered glass will shatter when attempting to drill.
Easiest way to determine this (although not foolproof) is to look at the glass through polarized sunglasses. Tempered glass looks to have an oily film through polarized glasses. Regular glass does not.

Thanks for the reply. The tank (120) is already drilled on the bottom. I am interested in drilling the backs on both, not the bottom. Thanks again.
Jim

 

[ndrwater]

No worries. My bad, when I first read your post, I understood you also wanted to drill the bottom. Here is a link to a BRS video showing drilling a tank for an internal overflow.

 

[JMM744]

Going to run this through again. Thanks, Jim

 

[dbl]

Drilling not a big deal if non-tempered glass. Plenty of video help out there for that. However...

Having your return outlets at the bottom of the tank is not a good idea in my opinion, unless you have a sump that will hold the entire contents of your tank. The drain down during power outage, pump failure, etc. will syphon to the point of your return line discharge level.

Some will say this can be handled by drilling a small hole in the return line just under the water line, but it's simply to risky in my opinion. If you forget to regularly clean it, or if it gets clogged in any way, you're going to have a problem if the return pump shuts down.

Again, my opinion, but keep the returns high and put a small powerhead towards the bottom if it's something you want to do. Or simply position your other in tank flow to keep the debris suspended.

Just my $.02.

 

[JMM744]

Drilling not a big deal if non-tempered glass. Plenty of video help out there for that. However...

Having your return outlets at the bottom of the tank is not a good idea in my opinion, unless you have a sump that will hold the entire contents of your tank. The drain down during power outage, pump failure, etc. will syphon to the point of your return line discharge level.

Some will say this can be handled by drilling a small hole in the return line just under the water line, but it's simply to risky in my opinion. If you forget to regularly clean it, or if it gets clogged in any way, you're going to have a problem if the return pump shuts down.

Again, my opinion, but keep the returns high and put a small powerhead towards the bottom if it's something you want to do. Or simply position your other in tank flow to keep the debris suspended.

Just my $.02.

My thought was to use a check valve in the return lines in case of a power failure etc.. I realize that there is a chance of one or both failing . Thank you for your advice David and I Will certainly consider it. Thanks again, Jim

 

[dbl]

I personally wouldn't rely on a check valve either Jim. I'm really not trying to squash your plans here, just trying to protect your floors.

Small snail, debris, whatever will prevent a check valve form properly seating/sealing. In my humble opinion, the only true fail safe method of limiting back flow is to keep your return lines just under the water surface. Again, just my opinion.