@420benz I'm assuming you can see a visible tear or hole in your liner? I would not recommend either of these products. I think the best way to fix a visible hole or tear is with a scrap piece of liner and some PL roofing sealant. Clean the spot really well, slather on the goop and lay that piece of liner over the hole. Another option is an EPDM repair kit - same concept. You'll get the sealant and some pieces of EPDM to place over the hole or tear.
You have already done the hardest part...finding the tear.
As stated, some members have had good results using PL-S30 which comes in a tube that fits your caulking gun. Spread the PL, and slap a scrap piece of liner on it. If possible, clamp it between two pieces of wood overnight.
If your liner is in fact EPDM rubber, you can buy a specific EPDM patch kit which will probably include a patch, primer and glue. Be sure it's EPDM. Using an EPDM patch kit on a different material most likely will result in failure.
I hope your tear is small and you get it patched up good and permanent.
The patch kit is probably your best bet. I used a kit to repair a hole chewed by some little critter with bad taste. I can't imagine EPDM tastes very good. The patch has been there for 6 years and still going strong.
Sorry I misled you but what I meant is that the leak is somewhere around that level. I have no idea where the leak is.I planed to lower the water level past where the level stopped and paint all around the pond with a waterproof sealant.
Oh, I thought you found the source of the leak. Bummer. Those things can be hard to find.
In trying to locate the culprit, you might ask yourself how fast does the water escape? How many inches are lost within a certain period of time? If it's a lot, then it's probably a decent size hole which you should be able to locate by feeling around with your hand.
I guess you let it leak to the point where the leak stopped. As long as you are certain of this, you have most likely have nail it down to that level.
Are you sure it's not coming from any external hoses, piping, waterfall or skimmer? A large percentage of leaks develop around waterfalls.
If you shut down the pumps and get lucky enough to have no wind. you can drop leaves etc see where they head . You can feel the liner where your leak is the soil should be soft . They also have dies you can buy that show flow again for the pumps off.
Ahhh... in that case, you may not have a leak in the pond itself at all. Your first stop should be the waterfall - that's where most "leaks" occur. Edges can get low, rocks can shift, etc. Turn it off for 24 hours and see what happens to your water level. If the water continues to drop at an excessive rate, then you may have a leak in the liner.
Next most likely spot is the plumbing, generally the connections. Check everything along your plumbing lines, looking for wet spots where you shouldn't have water.
LAST thing you should suspect is a leak in the actual liner. It's actually the least likely reason you would be losing water in your pond. But definitely don't go to all the trouble of sealing the liner because you THINK it's leaking.
OK I did all of the above. I pulled the plug on all filters even the two aerators.I raised the water level higher than normal and again the level dropped down to the leak level in about 45Min. My plan was to first mark the leak level on the liner then empty and clean the liner and carefully look for the leak. If i can't find it i planed to use a waterproof sealer all around the leak level.
How big is your pond that the water level dropped to where you think it's stopping / where the leak may be?.
At this level is there any plumbing .? skimmer? where the liners over lap? again look and also feel your way around as the leak should be softer then the rest of the pond
Before you do that, carefully check around the edges of the pond - see if there are any low spots where water could just be escaping over the side. Even an area where water is being wicked out by a fold in the liner can result in significant and surprising amounts of water loss.
Just trying to save you some hard work. Like I said up there an actual hole or tear in an EPDM liner is USUALLY not the cause of sudden water loss in an established pond. Generally you would know that something sharp - like a falling rock, someone walking in the pond stepping on sharp rocks or a even dog's claw struggling to get out after falling in - potentially caused a tear or maybe you know you had burrowing animals that could be chewing at the liner from the back or underside. Liners don't just rip or tear on their own - unless you have a construction issue where you had a stress point from a liner being stretched too tight up against something sharp, or something sharp hits that stretched liner.
@420benz you're going to have to do the hard work of actually pulling back your edge and looking for any low spot, if you suspect the pond is leaking. Have you confirmed no plumbing (you DO have plumbing else your wfall would not work) or wfall leak by turning them off, filling the pond, and waiting for final stop point? If this 2" lower level is where it stops, that's where you look, whether by pulling back the edge and inspecting or actually looking for a tear/rip/chew hole. Is your wfall totally lined underneath? Is the liner ONE liner or two? Does the pond liner, if separate, go up high enough under your wfall liner so as not to wick? Is your autofill system the level at which the water stops leaking? Maybe it's siphoning back? I'd not have such a system actually physically connected to the pond but instead, with an air gap between.