i surely hope you two are right. problem is, as i've seen in not only my pond (before i fixed it) but in a couple other ponds, is they hold fine til a certain level, then when it goes above that level, it cant hold and drops real fast back to that certain level. in these cases its either a leaking layer in the sides, or the volume increase and subsequent weight of water is able to hydraulically push itself out through bottom.
i wouldnt waste any money on bentonite either, and maybe i'd wait a year to see if its just needing to saturate the surroundings, but if it keeps acting that way, its leaking, and will need a better fix than just dumping bentonite in (MO). jeffh, the water pressure itself will not help compact the substrate, but it can help move fine grain materials into cracks and help seal a pond in the right situation.
