I have used 3 methods for leveling tanks. Which one depends on two factors. The first is the stand itself and the second is the nature of the floor.
This house has no basement and is build on a concrete slab. This means we have covered the slab with a wood flooring. The design of the house is that it is a split level with about a 2 foot difference between the two levels. It also have very high ceilings with the peak of the ceiling being over 15 - 17 feet above the floor depending on which level. Yhe concrete floor gets pretty cool to cold.
As a result for many years all the flooring was made of hardwood tiles which had a 1/4 inch of styrofoam on the bottom to help insulate. These tiles are common in apartment buildings but not so common in individual home and these days are almost impossible to find. Last year we replace the flooring on the lower level. I have never had tanks on the lower level. I also have tanks in our second building which has plywood flooring. In my fish space there the floor is cover in vinyl self stick tiles. Finally, I also used to put simmer tanks up one the screen terrace which has ceramic tiles.
As for stands I have three types. One are he tradition iron stands which only support the frame on a tank. The other are wooden stands which I have built myself with one exception which are my two tank in-wall tanks which I hired a skilled carpenter to custom build for me. These only show the glass front of the tanks. The frames and edges are hidden. This set-up was built perfectly level and 20+ years later still are.
Most of my wooden stands only support tanks on 2x4s on edge which means the support only under the frames. I initially built a few wooden stands which had a full sheet of plywood as the top. I no longer use any of those. But when I did they were always leveled using shims under any of the 4 legs needed to level the tank. This is also how I leveled a few of the metal stands. Because of the flooring the tiles under the legs can compress from the weight over time. Some of them have a small block of oak under each leg to help distribute he weight but they still needed shims in many cases.
The issue with the wood stands with the top only supporting the frames but the bottom being a full plywood surface is that the 2x4s on edge do not offer a smooth surface. I wanted to compensate for this. My solution was to use Self Adhesive Foam Tape Weather Stripping. The adhesive is only sticky on one side. This comes in a vaiety of widths and thicknesses. I would use 11/ to 1 inch wide foam which a adhered to the surface of the 2x4s where the tank frames would rest. The weight of the tank would compress the foam where needed and the result was a leveled tank.
There is only one drawback to this. If I have to remove the tank from the stand the insulation in places will stick to the frame of the tank despite no adhesive involved. This is due to how much weight sits on the foam and how over time this cause it to attach to the tank. This means one must spend time scraping it off. I do not move the stands much and I only discovered this issue when I was tanking tanks down for good and wanted to be able to sell them. I hade to remove the stuck on foam.
But my primary leveling had been the wooden shims. I will set the tank on the stand an partly fill it wih water to make it heavier. Then I do the shimming, drain the tank and proceed to set it up in the normal way. Substrate first, water next. For most tanks the water may go in in stages so I can add decor and live plants.
It is a lot easier to plant a tank in stages, IMO. I will put in about 1/3 of the water and them plant the foreground. I then add more water and plant the mid=ground and finally I put in more water to add in the background plants. I also add a lot of the decor during the first two plant stages. It is hard to add taller plants in the rear if there is not enough water to support them fully. Otherwise, they useally will flop over. This can be a real PITA in getting the look the way I want it.
Part of the issue I have to handle is that the early flooring tiles with the Styro under them is they compress differently over time and I may have to reship some to fix that. I have learned always to keep shims handy. Also, the summer tanks going onto the tiling on the terrace where level floors were not as critical as those in the house proper made it necessary to ship almost all the stands. the floor is gently sloped and also had minor depressions where what can puddle as a good rains can cover the floor with water. The furniture etc on the terrace is piled into a corner and the cushions are removed in the early fall and put back in the late spring. The floor needs to be hose down and washed due to the spring pollen and year round dust than can accumulate.
Here are some pics which will illustrate the above info:
150 and 125 on stands I built in place. Note the black line under the tank framed stand. It is the weather stripping. The 125 has a black frame making it impossible to see the stripping.
Terrace stands with shims.
Wood stand in the fish space
Another homemade wood stand on the styro backed wood tiles. The from left leg has hard to see shims under it.
(edited for a ton of typos)
