to drill or not to drill that is the question

stevieduk · Mar 14, 2016

I wanted a 8 foot tank but the cost of it was to much so I got myself two 4 foot x18x24 and pt them side by side. Now im wondering if I should silicon the two end glasses (were the tanks touch together), and when the silicon has cured ,drill a 5 inch dia hole to connect up the two tanks , or would the water pressure be to much for the glass.
They are both made with 6mm glass and have strapping around the top
any thoughts..........apart from DONT

tgp4274 · Mar 14, 2016

hhhhmmmmmm......

20LogR · Mar 14, 2016

If you do, I would drill the hole up high on the tank. IMO sounds like a bad idea, If anything goes wrong with the bulkhead you could end up cracking the glass and would have 2 leaky tanks. Why not just put them both on one sump?

nervousmonkey · Mar 14, 2016

Water pressure isn't an issue since you would have equal amounts of water on both sides.
I wouldn't silicone the two tanks together but would join em by a big bulkhead; I'm sure there is one that big. I'd be more worried about the stress on the glass from having so much of the structural support of the glass drilled out but with a good bulkhead it could hold. I say go for it, just get a powerhead to get water transferred from one tank to the other and put the overflow on one of the tanks so water has to flow through the hole. Interesting idea....

20LogR · Mar 14, 2016

I'm just a systems engineer, not a real engineer so I may be completely wrong, but I would think that getting the pressure between the two plates of glass to be equal and distributed equally would be near impossible.

What about the bottom of the tank? I assume these 4ft tanks have rims? Are you going to cut those away to push the glass together?

My suggestion would be the combined sump, OR another suggestion would be to use two bulkheads and a short piece of PVC and leave a gap between the two.

nervousmonkey · Mar 14, 2016

If there is a gap between the two plates of glass you're right but if they are siliconed together acting as one piece, there would be natural and equal distribution

Aaron hacking · Mar 14, 2016

By strapping around the top I'm guessing it's the same as a tank with a rim? wouldnt that create a gap along the whole sides when sitting flat? I guess with enough silicone you can fill any gap but then drilling through gobs of silicone becomes a problem... What about a water bridge?

stevieduk · Mar 15, 2016

well the strapping /glass strips round the tops are internal so there is no problem getting the tanks to butt up together.
when I said about the pressure on the glass I was meaning the rest of the glass, being designed to take the pressure of about 60 gallon, and now having to take double that

reefwiser · Mar 15, 2016

Would will need to use a bulkhead fitting between the two tanks put one near the top and one towards the bottom.

ReeferBob · Mar 15, 2016

I would suggest you drill a hole in the end of each tank, put a bulkhead on each and connect with flexible PVC. This will keep the water level the same in both tanks regardless of where the holes are. Then use a single sump returning to one tank and the drain from the other into the sump.

Aaron hacking · Mar 15, 2016

stevieduk said:
well the strapping /glass strips round the tops are internal so there is no problem getting the tanks to butt up together.
when I said about the pressure on the glass I was meaning the rest of the glass, being designed to take the pressure of about 60 gallon, and now having to take double that

It won't increase the pressure any, because they will be sitting level next to each other. You effectively only increase area that the water volume is filling. If you increase depth it would increase pressure. Even if you had a tank 50' x 50' x 24" deep the pressure would be no greater.