A tank is levelled before it is filled, decorated or stocked, because once water is inside, the weight makes every later adjustment risky. Put the stand in its final position first, set the empty tank on it, and run a long level along the front rim, down both sides and corner to corner. Where a reading is off, the correction goes under the stand's feet in the form of proper shims. The tank itself is never shimmed, wedged or twisted — glass needs to sit flat and fully supported along its whole base.
Why a Small Tilt Is a Serious Problem
Water does not spread its weight evenly in a tilted tank; it pushes hardest toward the low corner. That uneven load twists the cabinet, works constantly on one silicone seam, and leaves the opposite corner comparatively unloaded. On larger tanks the forces are considerable, and the failure it eventually causes is rarely a gentle leak — a seam under permanent strain can let go suddenly. A visible slope also shows in the waterline, so a tank that looks crooked against its own surface is telling you the load is crooked too.
What You Need on the Floor Beside You
A spirit level long enough to span the tank's width gives truer readings than a short one that rocks on the rim. Use purpose-made composite or hardwood shims that will not compress, crush or rot — folded cardboard, coins and offcuts of soft wood all flatten under load and quietly undo the job within weeks. If your stand's design includes a foam or polystyrene base mat, have it in place before you take readings, because the mat is part of the support system the readings assume. A pencil for marking which foot needs lifting, and a helper for sliding shims without rocking the stand, complete the kit.
The Order That Keeps It Simple
Level the stand on the bare floor first, before the tank goes on: floors slope, and it is easier to find that out now. Check the stand front-to-back and side-to-side, shim the low feet, and confirm it does not rock on a diagonal. Then set the empty tank on the stand, add the base mat if the design uses one, and take the full set of readings again on the tank's own rim — the tank is the thing that must end up level, whatever the stand needed to get there. Add substrate, then fill just a few centimetres and read again; weight settling into shims can shift things slightly. Fill halfway, read once more, and only then fill to the top.
Errors That Undo Careful Work
The commonest mistake is sliding a shim under one corner of the tank itself, which concentrates the entire load on that corner and defeats the point of the exercise. Levelling after filling comes second: a full tank cannot be safely lifted at one corner, and draining it to fix a tilt wastes the whole setup day. Trusting the floor because it "looks flat" is third — many floors slope gently toward a wall or a doorway. Finally, once the tank is level and filled, do not drag the stand to a new spot; even a short slide can pop a shim loose. If the setup ever has to move, it is drained and re-levelled from the first step.
That unglamorous foundation supports every later job in the tank; put a follow-up question to KinsLe's Kinny; he answers using the KinsLe Answers library.