The Inspiration - Everyone wants a bigger tank, right? I thought I’d be happy with my 90 gallon reef for a couple of years. I thought I would wait to see how life played out before investing in anything bigger. Maybe not.
I was in Big Al’s and they have an amazing 250G tank on display. My wife looked at it and said “that’s about what you want, isn’t it?”
The tank we were looking at was the Marinland Deep Dimension 250G with Starphire front and dual corner overflows. There is also a 300G version which is currently the largest tank available in mass manufacturing. While these tanks have some limitations, I must say they are absolutely beautiful. There are really only a couple of things which I don’t like about these tanks. The overflows are poorly designed. The cross bracing makes access to the tank awkward and limits lighting, and they are very heavy. Marineland told me that the dry weight of the 300G is 650 pounds.
I started asking around at various LFS’ (and searching Canreef) and the draw of the perfect tank began pulling at me. Why invest all of this time and money into something that is “nice”. It was at this point that I decided to have a custom tank built.
Tank Criteria – What makes a perfect tank? – I know there is no absolute answer to this question, but I had a pretty clear idea what I wanted.
• Designed for a wave. - This highlighted structural concerns for both the tank and the stand. It influenced the overflow design. This was the most expensive criteria and likely added over $2K+ to the build cost.
• Starphire on front and sides.
• Eurobracing with no cross bracing.
• Polished glass on all visible edges.
• Modified External Beananimal Overflow – Dead silent, completely stable and fully redundant.
Most importantly – If I was going to have a custom tank built, it had to be built on-site.
General Tank Specifications
Shape: Standard rectangle
Tank Dimensions: Length 72”, Depth 37 & ¼”, Height 28” panel + thickness of Eurobracing
Glass:
• Front - 5/8” Starphire Glass
• Sides - 5/8” Starphire Glass
• Bottom - ¾” Float Glass
• Back - 5/8” Float Glass
• Inside cleat - ½” or 5/8” Float Glass
• Top Euro - 5/8" Starphire Glass
• Overflow - ½” Float Glass
Edges: All visible edges polished. Micro beveled.
Bracing: Top Eurobracing, Bottom Cleats
Overflow: External Cup – 3 Bulkheads for Beananimal overflow
Extras: Polished Glass cover for overflow
Options: Black Silicon
Designing for a wave – Overflow size and placement
All else being equal, I would have designed a coast to coast overflow, or at least as long as I could possibly make it. I really believe this is the ideal design, but a wave creates a pivot point and a coast to coast overflow doesn’t really make sense here especially if the goal if for silent operation. I settled on a width of 1/3 the total tank length positioned in the centre. Also, making the overflow external makes sense for many reasons but is really a requirement for a wave tank.
Designing for a Wave - Glass Thickness
There is a good chart available at about.com here:
http://saltaquarium.about.com/od/pla...Calculator.htm
The first question is whether this chart considers bracing. The answer appears to be that the chart is for rimless tanks and at the recommended thicknesses does not require bracing.
For a 6 foot span at 27" high, the chart suggests that 16mm glass would provide a safety factor of 4.04. At 30 inches high, 16mm glass would provide a safety factor of 3.20 - The recommended guideline for the safety factor is a minimum of 3.8.
My tank Is 28" high, but I'm not sure If you count the bottom 3/4" as this is the thickness of the bottom sheet. Also, with the overflow being 2" below the top of the tank, the water level when flat would be just over 25" from top to bottom. Therefore, I feel reasonably safe in the 27" calculation.
Side Note: Starphire glass is manufactured at a thickness of 15mm where normal float glass is standard at 16mm. I do believe that the 1mm difference in thickness is worthy of consideration when compared against a recommendation for 16mm, although I can only guess at how the numbers would change.
The consideration for the wave was really just to include the eurobracing in the design even though the calculations suggest that 16mm glass is sufficient for a rimless tank. While I was never able to figure out the math or find a calculator that considered eurobracing, I figure it is sufficiently overbuilt. Further, I opted for cleats on the bottom, which are sometimes called bottom eurobracing. I'm not sure these were necessary either, but with them I am certain that the tank will be strong enough.
Google Sketchup is my friend - If you haven't worked with google sketchup, let me tell you that it is a lot of fun. I had to go through several of the available tutorials to figure it out, but the end result was really helpful in visualizing various different design considerations.
These are the pictures that I gave to the builder:
Figure 1: Showing the tank dimensions
Figure 2: Placement of the return lines (3/4” bulkhead)
Figure 3a: Showing the external overflow dimensions and the overflow cover (right).
Figure 3b: Showing the placement and width of the overflow.
Figure 3c: Overflow bottom glass – Dimensions and bulkhead spacing.
Note: Holes are to be drilled for 1.5” Bulkheads requiring a 2.5” hole.
I understand that the minimum safe distance from the edge that a hole can be drilled in glass is the radius of the hole. For a 2.5” hole, the radius is 1.25”. The math is pretty easy when the hole is centered (2.5” + 1.25” + 1.25”) and works out to 5”
Figure 4: Glass cut sheets.
Addendum I - If I had a do over
I love my tank, but perhaps it's not perfect. If I could do it over, I would have gone with a thicker glass (3/4" instead of 5/8"). I would have reduced the height by a couple of inches and I would have gone rimless. The Eurobracing would not be needed in this scenario and the added cost for the thicker glass would be offset by the savings in the Eurobracing.
Addendum II- Maybe not
I have changed my mind about the Eurobracing again. I love it. It's not just a structural thing. The bracing really helps to make to the tank managable. It creates a really nice platform for things like screen tops. It keeps splashes in the tank. It looks good too.