Busted Acrylic....

[BOTR]

In the process of making an overhead filter I managed to bust a large section out of a recently aquired acrylic tank. In an effort to avoid the same mistake in the future I have a few questions.

1) If a tank is bowed slightly, do you press it back in so that your dividers will join up with the walls, or do you just try to gob silicon in there to make up the difference?

2) Does age cause acrylic to become more brittle?

3) When using a long tank, would you cut the center brace out? Being that it wont ever really be full of water?

Here is my situation. I recently traded some livestock for an acrylic tank. I didnt ask many questions, other than to ask if it was able to hold water. I began work on the tank, drilled the side for 1.5" bulkhead. That went fine. Cut some material for dividers, drilled a drip plate and made an eggcrate base for my bio-media. Everything is going well. When I placed the first divider into the tank I siliconed the edge and put it in place. The walls were touching at the base and at the top. In the center there was about 1/4" gap from the tank being bowed out. I pressed the wall to make contact, and a huge piece craked out. I was stunned. Barely any pressure at all. And Bang! This is the situation that brings me to my questions at the top of the thread. I found out later that the tank was in use by the previous owner for about 8 years, not sure if age causes acrylic to become more brittle? Maybe even the type of lighting can affect it? ie. metal halides as opped to Normal Output fl.?

Not accusing anyone of any wrong, just really am curious for the future.

Will post pics soon.

Thansk,
Chris

 

[BOTR]

Pics.

 

[Red Devil]

That really hurts

 

[VLDesign]

Too mnay unkown variables with this.. Here is my opinion.


Some cheap thin acrylics do get brittle with age.

That tank looks like it was made out of 1/8" plexi which is way too thin and would not (Obviously) hold up to any kind of stress.

Also, on the next one, don't use silicone with acrylic as it won't adhere very well and it will eventually fail under any stress. Use Weldon acrylic glue.

If the tank is significantly bowed then that indicates it's defective or improperly designed. A slight bow can be corrected with clamps and dividers like you tried, but I would heat the entire area of the bowed acrylic up first to make it a bit more flexible. A hair dryer on the higest setting will work. Then you can apply pressure to the panel.

Never cut the supports off of any tank (glass or acrylic). You'll just make it weaker, no matter how much water is in it.

And MH lights are acrylic tanks worst enemy. Usually they are too close to the tank and over heat the acrylic, then it cools when the lights are off, then heats up again, cools etc etc and the materials become brittle.

I would say the breakage was due to inferior materials when the tank was made, nothing you did.

 

[Phixer]

Concur, in addition it's a good idea to keep your lamps far enough away from the acrylic to keep it from softening. Quality acrylic will not yellow however sometimes cell cast acrylic will craze (tiny hairline cracks inside the material) over time if the material used is too thin. Beware of acrylic tanks that bow too much. Many manufacturers use material that is too thin to save costs, eventually the tank will bow, become distorted and craze at the seams.