Neptune Aquatics

Modification on acrylic tank while full.

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sfsuphysics

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Ok, so some of you know of my great accomplishments in doing something experts would warn strongly against, example cutting into the tank and installing an external overflow when the tank has water in it. (This is just my little disclaimer, Don't Try This At Home) :D

Well my stony tank is a 100g acrylic tank, that's 6 feet long, but only 18" wide & deep, so I got length but I lose big time in other directions. Unfortunately this tank was made primarily for freshwater stuff I believe as a result the openings in the top are extremely mediocre, as they're made for dumping in fish food, and having a couple fluorescent tubes over it, not for high intensity lighting for corals and the like. What's even worse is the center of the damn tank has an acrylic piece that spans front to back, basically a brace so the deflection is minimized. Well unfortunately this means no light over this section, so I keep my low light LPS corals in this area.

Well I've had enough I wanted an open tank damnit! So first things first I had to increase the bracing around the top to keep the deflection at a minimum. So literally what I did is I cut strips that were I believe 1.5" thick and slapped them on top with weld-on in order to add more strength. I realize that the pieced together acrylic strips are not as strong as a single piece of acrylic, but I don't have that luxury to waste that much acrylic by buying a 6 foot by 1.5 foot piece and cutting out the center. There was some bubbling but its been sitting for quite a few months like that so I'm happy for now, besides the tank is only 18" tall so I'm not terribly worried.

Next step was to chop out the center, so as I'm over the tank with my circular saw cutting through the acrylic I'm thinking to myself... "Geeze Mike, high amp electrical tool over salty water, this probably isn't your most brilliant of moves you've done..." however I am typing this up, so obviously I'm still alive.

Ok enough of the chatting here's some pictures, I only cut the center out simply because I want to get a feel for what's going on as this was almost a spur of the moment "ok damnit lets just get this done how hard could it be..."
Needless to say I was awestruck by how much of a night and day difference it was to have all this open space! Now if I put a light over this part it'll kind of negate that feeling, but for now my first thought is damn I can feed my lps without having to stretch from the side, or CHRIST! I can finally scrape the acrylic in the middle!
p8200052ef0.jpg


Here's a kind of blurry, me stretching the camera to get a downward shot, picture. The yellow at the top right is a tang, the blue-green in the center is a colony of acans, and the purple along the top is coraline growing on the bottom :D Also you can see my coast to coast external overflow, which actually is acting as a brace along the entire back, so I'm not concerned at all about the deflection on the back side. The cuts are rough, but I figure that I need to smooth it with a router later (due to the incredibly sharp corners) so I'm not concerned about a jagged piece here or there... until I rip the hell out of my arm on it.
p8200053zf6.jpg


Now here's a shot where you can get an idea of how damn small the openings are, and that's a lumenarc mini over it, too much light is being lost because of a little bit of water on the top, quickly evaporates leaving a crusty white salty shield.
p8200056ps5.jpg


Eitherway I'll update later on when I finish it all up, I was just so shocked by how much more open the tank looks without that middle piece I had to share my story.
 
Mike,

Nice work. Was this the standard Tru Vu design? I've always wondered how much light all the acrylic takes away. Also, does your tank have one continuous piece for the vertical front and sides? Did you measure the deflection before and after? My 40 is 36"x15"16", so you think I could get away with a one piece 1/4" Euro brace?

Cheers,

Josh
 
I think it's a standard TruVu design, the issues with acrylic is first it's reflecting light, then if you don't keep it clean it blocks light, and eventually wouldn't surprise me if the structure of the acrylic changed under HID lamps such that it blocked even more light. However it's not enough that's there's a noticeable shadow or anything.

I haven't measure the deflection after yet, simply because I can't imagine how I'd do it (didn't want to build a rig just to get something to wrap around the tank) however there is no difference in what it looks like, in a few days I'll measure the distance between the corners of the cuts that I made to see if it moves though.

You probably could get away with a 1/4" Eurobrace in addition to what's there, that's pretty much what I did is I doubled the thickness of the bracing to compensate for the smaller width.

Phong, don't confuse bravery and stupidity :D
 
this is gonna end badly if that's a standard TruVu. The reason the top is like that is that is how it was enginereed. From talking with TrVu, Scott told me most of the load strength is in the top and enlarging the hole, or worse, cutting out the center brace will lead to failure. Not sure how long you have, but keep some buckets around :)
 
To follow up on what Gresham said. If I were in your shoes I'd double up on the top bracing mebbie to 3" in, use weldon 40 if you can get it, make sure you weigh the two components, and clamp real tight. The standard TruVu tanks are pretty flimsy to begin with, so be safe.
 
Well its not like I just cut the bracing out :p I did increase the thickness of the rim. But I'll probably toss a couple strips across the top to be sure, there is a tad of flex in it (to the point where I can squeeze the whole thing back, however over a 6 foot long tank that's probably not out of the question)
 
the buckling strain on a eurobrace is much greater when you double the thickness compared to doubling the span. If I understand what you did correctly, not only did you make this trade off, but you also removed the center which is a greater buckling strain relief. I would not sleep well at night. You really need some cross supports in there (as you said you may do).
 
Are there tables to what an "acceptable" deflection would be? The center is bowed out a little less than half an inch out further than the edges, granted that's over a 6 foot long tank.
 
Figured it'd be smarter to measure before I chopped :D

Anyways figured out an ingenious way to find out how much it's bowing out. Put the old piece of acrylic back into place! Taking into account the thickness of the sawblade it's only bowing an additional 1/4" from what it was before. Not too shabby, although I'll probably put a couple acrylic braces across the tank simply to let Tony sleep well at night :D

Gotta find me some clamps that are that wide first.
 
That's a quarter inch along the top of the pane in the middle of the tank (3 feet from one side). Normally the tank is 18" wide at the ends, and 18.25" wide at the center, now it's 18.5" wide at the center. (Measured at the top)

It's not the center of the middle part of the pane which is bulging out, but that occurs anyways since that would be the most flexible part of the tank (furthest from edges, furthest from any bracing), and quite honestly that bulge is not one I'm worried about at all.
 
[quote author=sfsuphysics link=topic=4378.msg53295#msg53295 date=1219359446]
It's not the center of the middle part of the pane which is bulging out, but that occurs anyways since that would be the most flexible part of the tank (furthest from edges, furthest from any bracing), and quite honestly that bulge is not one I'm worried about at all.
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well if the "buldge" is more extended wouldn't you have an outward force (like normal) and and additional leverage force along the joint to worry about?
 
I wonder if you could put in a couple stainless steel rods across the middle with tension bolts? Like how they retrofit old brick walls for earthquakes.
 
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