Slow Bizzare Leak....

I recently resealed a 150g tall, not much fun considering the 3' height on the tank.

It sat for 4 weeks dry as the Sahara and I was aghast to find a slow leak upon return from a week away. Nothing significant but it lost about 2's of water level while away.

Yesterday I drained and moved the tank out back, put it up on some jack stands, and thought I had easily found the source, lower back corner.

Alas, I place the tank on a slight angle with that side lowest thinking I can get under the tank and find the point of escape. Nope. It sat there for hours not leaking.

It only began to leak when I filled it up completely, but again from the same area, no visible water from any seams or joints above the bottom of the tank.

So, here's the question. Obviously there is a pinhole or some point of escape in the silicone. Has anyone had anything similar occur?

I used 100% pure black silicone from Lowe's simply to not have to deal with eventual algae stain in the clear silicone. This shouldn't affect performance as it's all 100% silicone.

Is it the water weight / pressure forcing the leak? Any thoughs?

Evaporation?

Do you have any young, thirsty children in the house who are familiar with climbing on chairs and love to use those bendy straws?

If you aren't seeing water on the floor, I would not assume a leak.