#*@%

Just finished plumbing my 20g long down to a 15g long. I used the glass holes 300gph overflow kit. Drilled 1 1/2 inches down from the top in the center of the tank. Fill it up with water to test for leakes and calibrate my T valve for proper return volume. Get every thing set and crack!!! Cracked from my overflow down to the bottom. Does anyone know what would have caused this and how to prevent it on my next tank.

 

Tanks that small use thinner glass and are more prone to breakage.  I would speculate in your case, it was the weight of the water that caused a chip in the outside of the drilled hole, to become a full crack.
I had the side of my sump crack (75 gallon - 3/8" glass) and after examining things, I believe that it was caused by stress from the plumbing.  The plumbing was putting pressure on the glass and because everything wasn't aligned to prevent the pressure on the glass, it cracked.  At least that's what I'm speculating happened.  I changed the plumbing, fixed the sump (by inserting a second glass panel inside using silicone to hold the two together) and things have been great since.
In your case, stress from plumbing may have been a contributing factor if you were adjusting a ball valve or something else at the time of the crack.  I guess the only advice that I can offer from my lesson is to make sure that there's no pressure whatsoever applied to the glass  from the weight or movement (i.e. vibration from a pump, etc.).  Use braces and tie-downs to hold the plumbing in place to prevent undue stress.
Lucky for you, I think that PetCo is still doing their $1 a gallon sale.
--AJ

 

Very true. After thinking about it im convinced it was the weight from the water flowing thru return pipe back down. The only thing holding it up suspended would be the bulkhead. Cant belive i didnt think to support the plumbing some how. Oh well like you said petco still has the sale so it was only a 20 doller mistake.

 

You didnt hard plumb from one tank to the other did you?

 

Yes i used 1" pvc for my return back down.

 

That was your problem.

You have to have some flex. I usually will use a hose to run from one tank to the other like that. Another thing you can do is run your 1 inch into 1 1/4. Dont glue it, just have the smaller pipe slip inside the bigger pipe.

I am not sure if this will work in your situation, but something to look into.

 

FWIW, I use standard SCH 40 PVC for virtually everything. There's a little Spa-Flex in there, but 95% is SCH 40 PVC.

--AJ