My waterfall is a flagstone slab that is balanced so that it tips slightly forward toward the pond and the other end comes up to rest gently under the lip of my biofilter (what Aquascape calls a "snout"). A fair amount of water also runs off the back end of the flagstone, and I'd like to seal this gap, but I think it's gotten too cold for the usual black foam to cure. Please tell me what you think of these ideas or suggest something better.
Use a hairdryer to cure the foam.
Silicone. But I'd rather not shut off the pump down for 24 hours to let silicone cure. I started over just a month ago, and I'm afraid that if the filter dries out I'll loose too much bacteria. I do have a check valve, but it doesn't work well enough to keep the filter full.
Bentonite clay. Will it stand up to running water?
Foam weather stripping wrapped in polyethylene as a temporary fix. But will it kill fish or frogs?
Rethinking things, I don't think I want to fix that heavy slab of rock to the snout of the filter at all. It's just weighs too much. Hence, I'm thinking some sort of foam or very soft rubber is the way to go. I'll just put it between the rock and snout and let the few pounds of unbalanced weight of the flagstone compress it. If a little water gets past it won't matter because it will still be inside the liner.
But what can I use? Is seam tape cushy enough? Will weather stripping kill my fish?
As long as the weight is supported then i dont see the problem with attaching the slag to the filter outlet.
Another option, if you werent bothered about it tipping the water out, then you could make a small rock wall around it using colour matching pebbles, slate, flint etc. and glue it around the sides and up to the filter outlet, using a product called Innotec Adseal, which will cure when wet, cold and will last alot longer than simple silicone.