Acrylic tank bracing question

[mgranato]

I have a custom display that measures 60x23x23 inches with 2 large (8x13) overflow towers in each rear corner. I over built it with 3/4" acrylic for the sides/front/back (corners reinforced with 3/4x3/4 gussets) and 1/2" on top and bottom. The top has 3 cut-outs with 3" rim going all the way around. The tank originally had PC lights for FOWLR, now I've 2x250 MH in Lumenarc minis. I was wondering if I could cut off the 2x8" struts defining the 3 openings, and leave the tank with only the 3" rim for top support? Or add a 3/4" x 6" euro type brace over the center leaving me with 2 large openings? Right now, the tank has 0 deflection/bowing, and I certainly don't want to risk any structural integrity, but I would love to be able to have the MH over water only - now they are sort of close to the bracing. I have the bulbs 16" above the water. Any advice would be greatly appreciated - thanks. If my description isn't very clear, I can take some pics.

Mike

 

[Acrylics]

Youcould remove the crossbracing and it would hold water, but would bow some. My thoughts go two ways on this; either place the bulbs towards the center of the tank but over the two outside openings which should be fine, or remove the two crossbraces and replace with one in the center as you were thinking. You can also keep the tank as is but move the lights much closer to the water level, I had bulbs as close as 3" above the water, just be sure the reflector is not over the acrylic crossbracing.
'course you could just get one more bulb/ballast set up as well since you already have the 3 top openings.

Hope this makes sense

James

 

[mgranato]

James, thanks for the response. Because of the two large overflows in the rear corners, the two outside openings are not that great (lots of light on the overflows not the corals). If I'm reading between the lines correctly, you would probably opt for the 1 strong center brace. That sounds like the safest option. That would certainly give me the opportunity to get the lights much closer to the surface AND away from the bracing.

The tank is in full operation, would there be a foreseeable problem with cutting out the current bracing AFTER the new center brace is installed? I planned on using a jig saw set on a slow speed setting to help minimize excess vibrations. Any other thoughts about the "how" to remove the current bracing?

 

[Anonymous]

This is 3/4 inch acrylic? Not 3/8 inch? I would think 3/4 inch might be strong enough to just have the 3 inch rim.

 

[mgranato]

Yes, all vertical panes are 3/4", top and bottom are 1/2".

 

[Acrylics]

James, thanks for the response. Because of the two large overflows in the rear corners, the two outside openings are not that great (lots of light on the overflows not the corals). If I'm reading between the lines correctly, you would probably opt for the 1 strong center brace. That sounds like the safest option. That would certainly give me the opportunity to get the lights much closer to the surface AND away from the bracing.

The tank is in full operation, would there be a foreseeable problem with cutting out the current bracing AFTER the new center brace is installed? I planned on using a jig saw set on a slow speed setting to help minimize excess vibrations. Any other thoughts about the "how" to remove the current bracing?

You are reading correctly
First the disclaimer; I do not advise you to modify the tank, esp while in operation, too many potential risks involved as I'm fairly certain you are aware.
That said, cutting placing the new centerbrace first and then cutting the old ones out is the only "safe" way to do it. If you cut the old ones out first, there will be a sudden increased pressure which could snap the top bracing esp at the corners. Placing the new brace first at least keeps the tank stable while cutting the old ones out.
Personally, I'd use a router to remove the old braces but a jigsaw will do. There shouldn't be too much vibration as the vertical panels will be adding rigidity to the top, just as the top adds rigidity to the vertical panels.

This is 3/4 inch acrylic? Not 3/8 inch? I would think 3/4 inch might be strong enough to just have the 3 inch rim.

It is strong enough to hold, but not *rigid* enough to hold at similar deflection rates.

HTH, JMO, etc., etc.,
James

 

[mgranato]

I did some measuring a little while ago - the temp of the acrylic brace closet to the light is at 120* inside the closed canopy (laid thermometer on the brace for about 20 min.). The rim surrounding the tank is actually 3.5" rather than 3".

With all that being said (and I certainly understand the disclaimers), would it be worth the risk (whatever size it may be) to replace these two braces with one thicker brace in the center? I'm not itching to do this, but I'd rather remove them with the other brace in place vs. the current brace failing do to heat with only the rim left for rigidity.

I'll make the final decision, but I'm looking for as much info as I can get from guys like yourself who've got experience with the material. Thanks again, its been a huge help.

 

[mgranato]

Pic of current situation...

 

[Acrylics]

Hmm, worth it?? I'll put my money where my mouth is If you were *my* customer, I'd do my best to try to talk you out of the idea and if asked to actually do the work - would refuse. Even a 5% chance of a screw-up is too much for my taste, and a screw up could easily be catostrophic. I can possibly guide someone how to do it with the least amount of risk but that doesn't necessarily mean it ought to be done.
IMO, you'd be better served by going with a different lighting set-up although I understand the extra cost is not insignificant. Three 250w HQI bulbs would be absolutely ideal with the tank as is. That said, 120F is within my tolerance for working temps under load (130-140F *max*) so if what you have is good and serviceable - don't fix what ain't broke.

Hoping you take this in the manner intended

James

 

[mgranato]

Thanks a ton, James. She'll stay as is. An empty tank, I'd probably try it - but a full tank (in the kitchen) would get me shot if there were ANY problems. Good point of view, I wouldn't take this on with someone else's tank, so I should probably leave well enough alone on mine.