What would be the most reliable and fish safe sealer, sealant,silicone to use between the liner and the bottom drain, skimmer,waterfall etc? I've been told to use shingle and flashing sealer, AquaScape black silicone, 3M Marine sealer, RTV silicone and many other products. I don't want any leaks if that's possible especially around the bottom drain. I don't mind spending money for good quality sealer that won't kill the fish. Any help, personal experiences would be appreciated.

If you use silicone from the hardware store be sure to use a CLEAR Window and Door variety. The danger is when you use a silicone that is designed for kitchens or bathrooms. Often times there is a mildew resistant compound they mix in with the silicone for kitchen and bath that is TOXIC for fish!

Typically we are using silicone (RTV) on skimmer face plate and waterfall weir spillways. On our bottom drains we use a POLYURETHANE Sealant. It is for roof & flashing.

I don't know the brand off the top of my head but the variety we use when dry has a bit of flexibility. Maybe you can make it out from the photo. There are polyurethane sealants that dry hard as a rock and those are the ones you want to stay away from! You will see them names Construction Adhesive Polyurethane. The need for the flexibility allows for slight movement of the Earth, settling of soil, expanding and contracting from weather and such.



The Pond Digger

Check out the Aerated Bottom Drain Demonstration post in the Construction & Design Forum for more details on installing bottom drains.

The Pond Digger

I contacted the help line, 800-624-7767, for the Polyurethane sealer (OSI Pro RF140) that you suggested for the bottom drain and I was told that this sealer was not to be used underwater and would eventually begin to break down. I was also told that the curing of the Polyurethane would release toxic byproducts which could be toxic to the fish. So now what could I use that would be fish safe and long lasting?

99.9% of the polyurethane is not submerged underwater but sandwiched between the liner and the bottom drain. You'll be golden! Any toxins must be gassed off by the time you add fish because we have never experienced an issue using polyurethane.

The Pond Digger

Here is the polyurethane that we use on installations. When it dries it stays flexible. We stay away from the types that dry hard.

The Pond Digger