I have used carpet for underlayment for all my ponds, including my 9000 gallon one. I'll use it for my new 20,000 gallon pond too. the only people I have ever heard complain about it are people who sell underlayment. lol!!

I used commercial pond underlayment. It's similar to the weed control fabric used when landscaping. I have rocky soil, so I installed a double layer of the pond underlayment on top of a layer of professional weed control fabric.

The underlayment is designed to be highly resistant to mildew and rotting. It also guards against roots. I thought it was worth the extra money at the time.
If you think about the investment you will make in your pond. A tear in your liner could cost you the liner, fish, plants, and pumps. I'm all for DIY and saving money, but you have to look at the consequences as well.

I used carpet as well as the underlayment. We have very rocky soil here and used the underlayment over the carpet as insurance.

most modern carpet is synthetic, so is also resistant to rotting. And it doesn't matter if it molds or mildews....it's under the liner! Nothing beats a good thick carpet for protecting the liner from rocks. And it's free.

I didn't know carpet was free. I need about 200 sq.ft. LOL where do I pick it up?

Seriously, underlayment was relatively inexpensive when I purchased it for my pond. That was a while ago, but I'm sure it's still reasonable.

I was more concerned with rocks and roots tearing the sides of the pond liner. I think the underlayment fabric is superior on the ledges and plant shelves. I was also concerned with carpet riping, or becoming unwoven. Especially if your piecing it together.

My pond liners extends well beyond the water level and my underliner extends beyond the rubber pond liner. That's the area I would worry about mold.

Hi
Recently tore down a 5x10x3 deep above ground that has been running since 1982. I used a fiber glass tarp and I was amazed at what good condition it was in after all these years was even still flexible!! Had an invasion of strangler fig and marshmallow .Though the roots had grown both inside and under the tarp it had not been penetrated anywhere. nor was there a tear even on the bottom folds.
Needless to say I replaced with another tarp lol.
gary

Johnkr, just let your local carpet store know you want some and when they tear out old carpet, they will be thrilled for you to take it. It saves them dump fees and also keeps it out of the landfills, which is a good thing!!

Before burying carpet in your yard, please consider that you are also burying highly toxic chemicals that will be released into your soil and water table. Adhesives, flame retardants and stain protectors like toluene, benzene, formaldehyde, ethyl benzene, styrene, acetone, as well as a host of other chemicals, are used in carpets.

You know, like when they were released into your bedroom and the other sealed up areas (called your house) where you lived for years.

Are mosquito discs okay for tadpoles, etc? Does it only kill mosquito larvae?