Cut slit in back of acrylic tank for external overflow?

twahl · 12/30/2018, 10:08 PM

I'm looking to get back into the hobby and I am going to be buying a tank in the next month or so. I've been doing a bit of reading and I've decided I want to go with an external coast to coast overflow off the back of an acrylic tank. I'm looking to get a 36x18x30 high tank, and I'll fabricate my own overflow. I'm wondering if I could cut a 1 inch wide slit about an inch below the rim for a weir. Originally I was thinking of cutting a 24 inch slit, but I think that there might be structural issues doing that. Now I'm thinking of cutting two slits maybe 10 inches wide leaving a 2 to 4 inch piece in the middle to carry the load through from the bracing above. Does this sound like it would work or am I missing something? Any help would be appreciated. Thanks

laverda · 01/18/2019, 07:48 AM

I wanted to do the same thing. A new custom tank was not in my budget. I would probably do three 6" slots with 3-4" between them. You could overlap another peice of acrylic on the outside to increase rigity. Also the external box will help too.

mcgyvr · 01/18/2019, 08:07 AM

Without (at the very least) seeing a picture of said tank we can only make total guesses/gut reactions..
What you are describing can certainly work just fine in some situations and may be a potential problem in another..
If you want us to fall to one side of the fence or the other I will fall on that "should be just fine" side based on what you have described so far and the mental picture I have made in my head

Daddi0 · 01/18/2019, 08:57 AM

For what it is worth, I was always taught to make round corners and smooth/finish the cut outs to prevent future cracking.
Cheers! Mark

john08007 · 01/19/2019, 09:52 AM

Instead of making a horizontal cut i would think a jig could be fabricated to make a lot of 1" tall 1/4" wide vertical cuts giving you the wier you are looking for, i would also think this.is less likely to clog and be more structurally strong

FamilyTank · 01/20/2019, 05:54 PM

Seems like it should work. Maybe a series of 1/2" holes?

theatrus · 01/21/2019, 03:29 PM

If the tank is eurobraced, then don't do that. If its rimless, you can, but there will be significant bowing difference between the bottom and top.

1234 · 01/22/2019, 05:30 AM

If it were me , I'd make a box for the internal overflow and just put in some holes for the BH's, his way no compromise to the tank.

sfsuphysics · 01/22/2019, 05:22 PM

So I did this some years back with a 180G 4' x 3' x 2' tank, and this wasn't very thick acrylic either... think it was a TruVu tank and you know those guys totally skimp on acrylic thickness. But put the tank on the front and took a circular saw along the whole thing. My thinking at the time was that the external box is going to be welded to the back along effectively the entire length of the tank and this would supplement the lost strength due to the cut (yeah it had an obnoxiously large eurobrace, but again thin). I don't go exactly to the edge, but the slit was a good 3 feet wide. It worked fine and if I were to do it again I'd use thicker acrylic for the external box.

12/30/2018, 10:08 PM	#1
twahl Registered Member Join Date: Jan 2010 Location: Utah Posts: 36	Cut slit in back of acrylic tank for external overflow? I'm looking to get back into the hobby and I am going to be buying a tank in the next month or so. I've been doing a bit of reading and I've decided I want to go with an external coast to coast overflow off the back of an acrylic tank. I'm looking to get a 36x18x30 high tank, and I'll fabricate my own overflow. I'm wondering if I could cut a 1 inch wide slit about an inch below the rim for a weir. Originally I was thinking of cutting a 24 inch slit, but I think that there might be structural issues doing that. Now I'm thinking of cutting two slits maybe 10 inches wide leaving a 2 to 4 inch piece in the middle to carry the load through from the bracing above. Does this sound like it would work or am I missing something? Any help would be appreciated. Thanks

01/18/2019, 07:48 AM	#2
laverda Registered Member Join Date: May 2003 Location: Anaheim, CA Posts: 6,902	I wanted to do the same thing. A new custom tank was not in my budget. I would probably do three 6" slots with 3-4" between them. You could overlap another peice of acrylic on the outside to increase rigity. Also the external box will help too. __________________ 240G mixed reef, 29G SPS/LPS clam tank, 50G mixed reef Current Tank Info: 300g mixed reef, 50g cube

01/18/2019, 08:07 AM	#3
mcgyvr Registered Member Join Date: Sep 2003 Location: North Carolina Posts: 20,050	Without (at the very least) seeing a picture of said tank we can only make total guesses/gut reactions.. What you are describing can certainly work just fine in some situations and may be a potential problem in another.. If you want us to fall to one side of the fence or the other I will fall on that "should be just fine" side based on what you have described so far and the mental picture I have made in my head __________________ Who me?

01/18/2019, 08:57 AM	#4
Daddi0 Registered Member Join Date: Sep 2017 Location: Redwood City Posts: 1,354	For what it is worth, I was always taught to make round corners and smooth/finish the cut outs to prevent future cracking. Cheers! Mark __________________ 2x 65g displays with a 30g cryptic refugium and 30g sump - 55g reef 30g Bio-cube reef - I.M. 30g reef - 45g freshwater

01/21/2019, 03:29 PM	#7
theatrus 100-mile-commuter Join Date: Dec 2004 Location: almost nevada Posts: 4,721	If the tank is eurobraced, then don't do that. If its rimless, you can, but there will be significant bowing difference between the bottom and top. __________________ Custom electronics purveyor. blueAcro.com Current Tank Info: 90g SPS+mixed reef (10 yrs): LEDBrick LEDs, 40g custom sump, Ca reactor, chiller, Vortech, lots of custom electronics

01/19/2019, 09:52 AM	#5
john08007 Registered Member Join Date: Feb 2008 Location: Myrtle Beach SC Posts: 307	Instead of making a horizontal cut i would think a jig could be fabricated to make a lot of 1" tall 1/4" wide vertical cuts giving you the wier you are looking for, i would also think this.is less likely to clog and be more structurally strong

01/20/2019, 05:54 PM	#6
FamilyTank Registered Member Join Date: Apr 2016 Location: Downriver,Mi Posts: 226	Seems like it should work. Maybe a series of 1/2" holes?

01/22/2019, 05:30 AM	#8
1234 Registered Member Join Date: Oct 2003 Location: Portland,OR Posts: 769	If it were me , I'd make a box for the internal overflow and just put in some holes for the BH's, his way no compromise to the tank. __________________ I'm out of my mind, Please leave a message Current Tank Info: 225gal diy 60"x36"x24"

01/22/2019, 05:22 PM	#9
sfsuphysics Registered Member Join Date: Jan 2004 Location: San Francisco Posts: 9,103	So I did this some years back with a 180G 4' x 3' x 2' tank, and this wasn't very thick acrylic either... think it was a TruVu tank and you know those guys totally skimp on acrylic thickness. But put the tank on the front and took a circular saw along the whole thing. My thinking at the time was that the external box is going to be welded to the back along effectively the entire length of the tank and this would supplement the lost strength due to the cut (yeah it had an obnoxiously large eurobrace, but again thin). I don't go exactly to the edge, but the slit was a good 3 feet wide. It worked fine and if I were to do it again I'd use thicker acrylic for the external box. __________________ Mike