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Skimmer was installed seven different kinds of wrong. How do I fix this?

Subject: Skimmer was installed seven different kinds of wrong. How do I fix this?
by Otter on 31/10/2007 10:00:21

About two years ago we bought the house next door for my mother complete with a two or there year old liner pond. Though the previous owner was a landscaper, he didn't have any experience with ponds, and between his ignorance and my own, I've had quite a bit of trouble. I do love having the pond, though, and I'd like to put it right. Currently it's leaking at both the waterfall and the skimmer, and I have many questions before I go on with the repair. Unfortunately, the weather usually turns here in early November, and I'm running out of time. I suspect I've got less than a week to get this repair done if I don't want to work in the cold and set up some sort of tent if I use sealants that won't cure at low temperatures.

I'm not sure what caused the leak at the skimmer. There was not enough slack in the liner, hence some of the weight of the water was hanging from the inlet. Also, the inlet is warped (perhaps from over-tightening the screws?). The body of the skimmer is bowed in one side as well, so perhaps shifting earth warped the whole thing badly enough to break the seal. And one of the the aluminum thread inserts came out when I disassembled the inlet. This was directly below the inlet where it's hard to see the inside wall with the plate installed, and for all I know, it was loose before I took a wrench to it. There was some evidence of erosion down the front of the skimmer below the inlet, but I'm not sure if that was from the leak or from rain water washing down the hill behind the skimmer. The pond has always had a very slow leak, and the previous owner installed a float valve filler to compensate. It's gotten worse now, though, and letting filler run produces frightening water bills. How do I fix this mess?

The more I think about it, the more I think I must get more slack at the skimmer. Am I making too much of this?

By adding some earth under the liner, I was able to get about one cm of slack at the inlet. I don't really like this, though, because it makes working with the bottom row of screws awkward and may impede flow a bit when the surface is frozen. Also, if there is any further settling, the liner will start pulling on the seal again.

The only ways I can think of to get the slack is to move the skimmer inward (in which case, I'd replace it), or add a new piece of liner. I've been advised against adding a seam because the old and new liner might expand or stretch differently and break the seam, and because I won't be able to lay the pieces out on a flat surface to join them. But perhaps I could join old and new liner with a system of plates. I'm envisioning three plates:
Plate>Liner>Sealant>Plate>Sealant>Liner>Plate

Two experienced ponders on another forum suggested that I use polyurethane roof and flashing sealer instead of aquarium silicone to make the seal between the skimmer and liner. Does that make sense? Would it really make a better seal, and would it be safe for the fish and other pondlife?

Do I need to be concerned about what alloy aluminum fasteners are made of, or will anything from the hardware store do? Though the rest of the screws seem to be in fair shape, the head of the screw next to the one with the bad insert was so thin I had to use an extractor to get it out. I'm not sure if it once matched the others or not, and I wonder if it was made of an inferior alloy.

If I don't replace the skimmer, I'll need something for the hole where the thread insert ripped out. I have a new aluminum machine screw and nut, but aluminum washers don't seem to be available locally and I've only got a week or so before the season turns. I also have an appropriate the screw, nut, and washer in stainless steel, but do I need to be concerned about galvanic corrosion of the adjacent aluminum screws and inserts?. The steel hardware wouldn't touch anything that's made of aluminum, but it would be much closer than steel and brass on the pump.

It's been suggested that I drill out all the old inserts and go with all stainless steel hardware? Is aluminum really that bad in ponds?

Or should I dig up the old skimmer and replace it? Because of the time crunch, I'd really rather not, but I do want this to stay fixed. If I can find a sturdier skimmer with a larger inlet and install it slightly inward to get some slack, it would solve a lot of problems. I would have quite a bit of digging to do, though, and maybe some large rocks to move in order to get the slack around the edge of the pond to move the skimmer forward.

Please lend me the benefit of your experience. I know just enough to know that I don't know what I'm doing.