personally, "id get that foam outta there asap" to answer ur ? lol.... so many people use it now under acrylics that not many people believe me.... until they have issues... then i get contacted with repair ?'s. been there done that myself just the same so i understand the discrepencies on this topic and have seen the resuls in person. Foam will not level ur tank, it may decieve you into thinking so but it comes down to the same principle of leveling a tank properly. leaning one way or the other will surely make the "bad side" recieve more pressure, leading to issues over time. as u say urself leveling a tank is known to be a major issue. this is the same topic imo. foam can crush/distort over time making air gaps u tried 2 eliminate in the first place or make the tank unlevel. alot easier to not use it from the start and level the tank properly out of the gate. May sound like a stupid refrence, but watch an episode of "tanked"... they glue a piece of 3/4" ply to the bottom of every acrylic tank they sell/set up. theyve been in the buisness long enough 2 have seen the results of a non leveled tank, im sure they didnt do this from the start. makes for easy shimming tho inbetween the ply and stand. Honestly its better to not use foam and fill in air gaps directly under the acrylic with shims, then to use foam and think uve solved the problem.
Another reason y it may seam right to use foam is alot of guys dont keep there big tanks for long... they may be set up for 1-2 yrs and run fine with foam for that said time until there moved and resetup, but leave one there for 10yrs next to one without foam and yes i guarentee there will be visual discrepencies in the seams of the tank on foam just as there would be doing the same test of a tank that is leveled properly next to one leaning to one side.
Everyone wants to set up there tanks asap... foam is a cop out to make an acrylic tank level. its not always easy to level large tanks so i understand. doesnt make it right tho. Getting a 4x8 or said piece of foam home and under the tank without crushing it in some spots is almost impossible, let alone placing a tank on it with a few guys. soon as its crushed/distorted u start losing support in those areas and over time that problem grows. im sure i sound like a broken record by now, just trying to help others with problems ive experienced myself.