What kind of Acrylic?

[otto486]

I'm looking for a solid 3/8 acrylic to use as a sump.

First off, is Acrylite a brand, or a type of acrylic?

I know plexi is out of the question.

How does LEXAN polycarbonate compare? I know it's ALOT more expensive, but would it be worth it?

And finally, what kind of Acrylic should I use on an internal over-flow box? How should I adhere the acrylic to the glass? Should I just use GE1200 series silicon to waterproof it and leave it at that?

[woz9683]

You want a 3/8" cast acrylic in most cases, although some people will build sumps out of extruded material.

Acrylite is a brand, which comes in different types.
Acrylite FF is extruded material, which might be okay depending on the height of your sump and the volume of water you expect it to hold. Acrylite GP is cast material, which is the better option for pressure vessels.

Plexiglas is not out of the question, it's just another brand of acrylic. I forget the designation for its extruded material, but the cast material is Plexiglas G. The only thing that makes this a less ideal option Acrylite is that Plexi is made in Mexico while Acrylite is made in the US. So, the quality isn't quite as high, but it is still acceptable.

Another good brand would be Spartech Polycast, it's probably the best material of the three.

Don't use polycarbonate. It would be a waste of time and money.

And the overflow box depends on how you want to build it, but if you already have 3/8" material for the sump just use some of the excess for the overflow box. And although silicon won't technically bond the overflow to the glass it will form an effective seal. Remember, the pressure of the water in the tank is forcing the overflow box against the tank wall, so realistically all you need to hold it in place is a decent gasket, and silicon does this just fine.

[otto486]

Wow, very thourogh, thanks! My concern with plexi is that I've heard it yellows over time. Is that true?

[woz9683]

First of all, since plexi is essentially the same as the other brands of material, this would effect all acrylic products.

From what I understand, UV light is what causes the yellowing of acrylic. In our applications, most high intensity bulbs are (or should be) shielded against the release of light in the UV spectrum. So, while yellowing is a possibility, it can be negated by proper use of light fixtures.

Furthermore, even if some yellowing does occur even with proper light usage and so on, it must be minimal at best. Consider the number of people who have acrylic tanks. If yellowing was a common issue, I think we would hear more about it and see many less acrylic tanks or at least many less satisfied owners.

[mountaindew]

this thread has about everything you will ever need to know about acrylic
http://reefcentral.com/forums/showth...hreadid=169326

[Acrylics]

Otto,
Michael pretty well said it all and correctly, he knows his stuff
FWIW, the yellowing is a non-issue with today's acrylic. The formulations were changed many yrs ago but folks won't let it go.

FWIW, Plexi-Glas MC is the designation for their extruded material (MC=melt calendar)

James

[woz9683]

Thanks James, I'm working on it.

I knew there must be a better reason we don't hear anybody complaining about yellowing these days.

[Acrylics]

Originally posted by woz9683
I knew there must be a better reason we don't hear anybody complaining about yellowing these days.

Yep, they took cadmium out of the formulations about 15yrs ago. Cadmium is very light sensitive and would cause the yellowing.

Good job on the explanation and the knowledge base

James

[woz9683]

You know where it all came from, like I said, I'm trying.

EDIT: And thanks for another little tidbit I can add to the noodle

[mountaindew]

Originally posted by Acrylics
Yep, they took cadmium out of the formulations about 15yrs ago. Cadmium is very light sensitive and would cause the yellowing.

Good job on the explanation and the knowledge base

James

James, your vast knowledge on plastics just amazes me.

i keep the threads you post in bookmarked and i even copy your replies to a word doc. just for quicker reference. again thanks!

[izzy_real]

James does know his stuff!

So does Michael! They've both added to my system's success, and they don't even know me! But their help was invaluable. These guys are why I keep coming back to RC.

[otto486]

Yea, before I even posted the thread I sent James a PM, I saw MANY of his posts in other DIY forums, and figured he'd be the guy to go to- It's good to know there's always people who are there to help.

[otto486]

O, and one more question, is extruded material still pretty effective for sumps (20-30 gallons), or should I stick with cast? The local glass shops are having difficulty finding what I need.

[woz9683]

Well, sumps in general have more reinforcement than your average tank (baffles, chambers, etc). So, yes extruded material can be used more successfully in this type of application. If you want to use extruded material you should talk to Marc (melev) or at least check out his site, www.melevsreef.com . I know he uses extruded material for at least some of his sumps, maybe all of them. I also think he tends to use Acrylite FF, which is considered to be the best of the extruded materials.

IME, if you want to try to find cast material, you need to find a plastics supply place. I've yet to find a glass place that carries anything other than extruded material, and most just look at you funny when you ask what type of acrylic they carry (which almost universally means they just carry extruded material).