Is it normal for acrylic top to bow?

[shaka]

I have a 140 gallon acrylic aquarium ( 60"x24"x22") that has bowed upward from the top. The tank is 8 years old. I have a 2 bulb T5 light fixture inside the canopy. There is a fan that circulates the air into the canopy. I believe the acrylic top panel 3/8" thick.

Is this normal or should I contact the manufacturer for advice?

 

[sail33]

Not sure what you mean. The side or front bowed out or the top bracing bowed up ?

In any case, yeah...contact the mfg. and take a picture to help explain to them.
Post it here too. Maybe some one will assist with advice

 

[shaka]

Sorry I can't post a pic.

The front and sides of the tank all seem fine ( no bowing or minimal at most ), but the top sheet of acrylic ( where the access openings are located ) is bowing upward. It's as though the top sheet is taking the pressure off the front and sides of the tank.

I realize that the front, back, and sides of an acrylic tank might bow ( unless it is really thick acrylic ) but is it normal to have bowing along the top of an acrylic tank?

The tank seems to be made of 3/8" acrylic all around.

 

[Phixer]

Unlike glass, acrylic will absorb water, and when it does it develops more elasticity.

Is your top section exposed to the heat given off by MH lamps?

If so, the prolonged radiated heat will cause the plastic to soften and warp. This combined with the absorbtion of water, continuous pressure and the use of material too thin for the height often results in the condition you described.

 

[nickjj]

I have an entire 3/4' thick acrylic 200G tank and the center section between two openings has bowed a little bit upward as well. I used to have MH and T5 lights and it was pretty warm above the tank surface.

As Phixer says it is most likely the heat that caused the distortion no matter the thickness. I've not had any other issues with my tank.

 

[shaka]

Thanks for the responses.

I don't run metal halides. I have a 36" 2 bulb T5 ( 78 watts ) light fixture in the canopy. I have a fan for ventilation. I used to have a 36" 2 bulb PC light fixture but I removed it. I didn't think my current light fixture would cause a heat problem.

Sounds like it is typical for the top panel ( top bracing ) of an acylic aqaurium to bow.

I guess I wouldn't be too alarmed if that is what happens to most acrylic tanks.

 

[tippmannsniper]

I have never experienced it, but a fellow reefer had the same exact issue for 2+ years and never had a structural failure, just a slight eye soar.. From a physics/engineering perspective, I'd agree with the previous explanations.. Post a pic if you can

 

[petere1989]

i'm having this problem. its not so much a problem but i am having the issue. i have a 40 gallon freshwater tank that the top is bowing. I guess it is normal?

 

[Phixer]

Thanks for the responses.

I don't run metal halides. I have a 36" 2 bulb T5 ( 78 watts ) light fixture in the canopy. I have a fan for ventilation. I used to have a 36" 2 bulb PC light fixture but I removed it. I didn't think my current light fixture would cause a heat problem.

Sounds like it is typical for the top panel ( top bracing ) of an acylic aqaurium to bow.

I guess I wouldn't be too alarmed if that is what happens to most acrylic tanks.

Bowing to some degree will occur, if excessive it often reveals structrual design deficiencies. Your probably fine if your not observing any separation or crazing at the seams.

Heat over time combined with continous hydrostatic pressure can cause this. If your not exposing it to too much heat, then we need to look at other factors such as the design in relation to the ammount of pressure. How tall is the tank? Is it a eurobrace design or solid top with access holes cut out?

Many tank MFGs underdesign by using material too thin, some will use different sizes for the top and bottom??? thinking those panels dont require as much strength as the sides. Over time these short cuts manifest themsevles through excessive bowing and or internal crazing. Sometimes yellowing when exposed to UV radiation for the cheaper brands. Proper thickness of the top panel is very important.

If it's not crazing or separating it should be ok. Bottom line is there really isnt much you can do about it other than lower you water level to reduce the ammount of pressure exerted.