Hmm I mat have found the leak.... it could be a leaky bulk head running down the back of the tank into the bottom trim and the dripping through the trim making it look like a bottom leak.
On a side note is it possible to not have traditional cycle when adding at least half live rock and sand and dosing seachem seed? I have been "feeding" the tank coral smoothie and I know I at least had sponge die off but I've seen no ammonia , no2, or no3. And I've seen lots of brittle stars , asterinia stars out and a Rhodactis mushroom is doing fine.
If you dose stability there Will still be some cycle , yoi will still get diatom bloom of the ugly brown dust but the cycle time is usually cut down to 14 days or less , I broke a tank down last year moved kept everyone in a bin over night and set it up a day later without the sand and using stability saved all my fish and soft coral , I gave away sensitive live stock