Yep, tank is in the ground. Pulled it out a couple days ago and no leak.
Let me explain it in more detail.
The tank can be filled in the evening the day before and I go out in the morning and see not much changed, if there was a leak I would have noticed a big change in water level. So I leave it for the day, check it around 7PM and see that all the water is just about gone (sometimes I wait until the next morning but that's always turns out bad because the
pump is sucking air).
We just recently got out of a big heatwave too, was 105-110 for a good week. Now were 85-90 (82 as of 11AM) during the day, but has been in the 60's at night now.
Could that be the cause?