Before laying on the base board, a very thin bead of silicone was placed along the top of the beams. This bonds the board to the beams and prevents it moving around as the glass base panels are slid into place at a later stage. This is also applied to the polystyrene board as well, especially seeing as this stuff slides all over the place when you try to slide glass across it. You'll note from the shot the sprit level. Don't trust all materials to be correct when building. its not impossible for the manufacturer to get something wrong, or you for that matter, so always check and recheck levels at each stage of the proceedings using a properly calibrated level. By this stage in the proceedings, the entire stand was within 0.5mm of square, and less than 1mm off level over its 6.5 feet of width..

In this shot also, You'll notice that there are several circles marked and some lines that are blanked out by wavy lines. These are the intended holes for the Closed loop outlets, and returns. At the back of the tank (nearest you in the picture) you have 6" holes for the 50mm (outlet) bulkheads, and at the front (farthest away) you have 4" holes for the 40mm (return) bulkheads....Now the wavy lines are important in that quite a few years back now in my engineering career, I learnt very quickly, that when working within a limited space, or within tight tolerances, always, always, mark off where you 'Cant' go and you'll minimise both costly and time consuming problems later. in effect, the lines you see are the 'no go' areas directly on top of the support beams.

In this shot you can  see the holes in the now silicone'd base board, and the overlaid cushion board. Plus you can get a feel for the size of the final tank dimensions. The cushion board is 1" thick polystyrene sheet. With tanks this large its essential to have a thicker cushion layer that can handle the weight compared to lighter tanks that commonly use a 6mm thick cushion layer (similar to ceiling tiles).. Remember though that you need to factor these items in when working out the height of your stand etc, if building a picture view tank. In this case the actual base of the tank ends up approximately 3/4 of an inch below the bottom edge of the opening the tank is viewed through at the front. You can see that lip in the shot above. This ensures you don't get to see any ugly base or silicone at the bottom of the viewing pane as its hidden from view.

Well, with that lot done, it was time to get some glass in there, so the two base panels were ordered and delivered by Greenburge glass in Southampton (the same guys that did my sump glass)...As with the sump, all edges were ground flat and had a chamfer on the edges. In this case though the chamfer was kept to a bare minimum to retain as much contact area for bonding as possible. (remember that on a 12mm peace of glass, a 1mm chamfer on each edge will result in your contact patch dropping to 10mm over all so this should be a consideration on pressurised joints like the base-side's etc.

The reason for two bases is that it makes the tank inherently stronger, and the risks of a rock slide damaging the base is minimised. In this case the inner panel is slightly smaller than the main base by the thickness of the side walls all round. This means that when the sides are fitted, they fit into an L shaped lip that bonds not only at the flat face to face contact point but also for 10mm up the side.

Suffice to say it didn't go totally to plan as there was a hiccup with the square-ness of the main base pane, so this had to be re-cut as it would have chucked the whole tank out and made building it square virtually impossible. Luckily though this was done free of charge so i cant complain about that even though it did hold things up for a couple of days. My initial plan was to bond both panes together and then drill strait through, but with the hold up, this meant it was better for me to drill the inner pane first and then drill through the base pane afterwards using the holes as a guide...Looking back on it now, this was actually a better idea anyway.

When bonding the two panes together, I simply raised the upper pane to give me access, and then ran a series of silicone beads forming a cushion for the upper pane to sit on. With each run, a small gap was left at the end to allow air out when the panes were brought together and compressed, without which, there is nowhere for the fumes to go and the silicone will take much longer to cure being in an air tight gap. Leaving these small gaps in the runs of silicone allows air and fumes to escape leading to a better cure and bond.. To prevent water seeping between the panes via the bulkhead fittings, I ran double circles of silicone around each hole. 1 ring several inches away, the other right at the edge of the hole forming a complete seal. As the top pane is lowered down any cushioning pads are removed, the pane is positioned centrally by nudging across the wet silicone, and then its simply a case of climbing on top to squeez the air out and to spread the silicone to form a good strong bond between the two panes. Surplus silicone that oozed into the bulkhead hols was simply cleaned off using kitchen towel ready for the holes to be chased through the second pane.

Hole cutting/glass drilling is covered in the DIY section.

With the base panels drilled and in situe, it was now time to turn my thoughts to another issue that would surprise many, and that's the forming of the aquascape 'prior' to the rest of the tank being built.

Continued on the next page.