Today I spent the day creating a base for my 1200L fibreglass fishtank. The fishtank is one of Murray Hallams designs from Aquaponics Made Easy. The base needed measures 1.2m x 1m in size and will fit nicely around the back of my garage. I have space there for 2 of the fish tanks so one day I am sure I will get another one! The base is really important to get right and level and in this case I will be making the base out of blocks and sitting on top of the blocks will be 70mm thick sleepers.
First thing I did was clear the existing pebbles that are in the ground and excavate about 10mm. The blocks themselves will be sitting on a base of crusher dust. Crusher dust is excellent because it is cheap, easy to get anywhere and compacts down. So you can easily spread it, them wack it down with something heavy like a piece of wood to compact it, and then place the block on top.
I made my measurements out from the garage wall as I wanted the tank to run parallel to the wall and quite close to it. So I made the measurements and hammered some steaks into place then attached a string line. You can see that the steaks are placed past the corners. This means that where the string lines intersect gives you your corner.
After placing the first block, you can then get a height for the top of the stringline. This allows you to easily set the height for all of the future blocks. You can see in one of the pictures a level that you attach to the string line that allows you to get the stringline level. Make sure that you make the stringline really tight!
I was constantly checking the levels! I found a mallet useful to make minor adjustments and my foot to make sightly larger ones - like if I had to make one end lower I would wack it with my foot.
Once I got a block level, I would then check it against another block by making the level go across both blocks. Sometimes I had to make a few minor adjustments, but most of the time I could get the heights correct thanks to the stringline.
If your blocks are level then placing the sleepers on the blocks, the sleepers should be level as well. So if you place a sleeper on and then the level shows an issue, then there may be an issue with the sleeper. It may be bowed or different thicknesses at each end.
These sleepers are 70mm thick hardwood. They come in 2.4m lengths, so cutting one in half would give me the 1.2m length I need. The first one I cut had one end which was less then 70mm thick. I didn't notice this until I placed the sleeper which went width ways. When I did that, it was then I noticed the difference in height between the two sleepers. This is something to be wary of with hardwood sleepers as they are only rough cut and may have issues like this.
After I was happy that all of the blocks were fine and the sleepers were all good, I then raked the pebbles up against the blocks so that they covered the crusher dust and gave a little support to keeping the blocks in place. After the tank is filled, there will be over a ton of weight pushing down, so those blocks wont be moving anywhere!
So that's it for the fishtank base. I hope this has been useful and if you have any questions, ask away.