I just broke down my 20L tank and moved the shelving to a different spot. I'm trying to decide how to utilize it. The bottom shelf needs to stay where it is for structural reasons. The options I'm considering are to leave the shelves where they are, lower the higher shelf and add a third, or raise the upper. I'm planning to use the 20L as a quarantine tank. If I leave it as is and put the 20L on the bottom, I may have trouble doing water changes. The second shelf is currently 18" above the first shelf, 24" above the floor. If I drop the top one 12" it will give me 24" to the top of the stand, so I could add a third shelf, although that tank would be a bit high maintenance-wise. The catch is that I'd want to use the middle shelf for something bigger, either a 29g a 30b, or a 40b, so I'd have to place the quarantine tank somewhere else or plan to drain and move it when I get another tank. I could put the larger tank on top, but it makes me feel uneasy from a balance point. FYI the shelving is a heavy-duty unit rated for 800 lbs (362 kgs) per shelf, although I like to keep the weight to no more than half the capacity. I also live in an apartment with asphalt tile over cement floors, so weight is not an issue. Any thoughts or suggestions are appreciated.