Unusual pool to pond conversion

[buster_harvey]

Hi folks!

I need some feedback.  I want to convert my in-ground kidney-shaped gunite pool into a pond, but without damaging the existing pool.  The pool has not been used or serviced for several years, so I expect most of the chlorine will have leached out of the gunite and evaporated.  What I propose to do is (1) vertically stand a perforated metal culvert pipe wrapped in filter fabric centered over the pool drain (like a vertical french drain) so that the drain is protected and I can drain the pool to the bottom if necessary; (2) fill the pool with crushed stone up to about 40 inches below the proposed surface (up to the top of the culvert pipe); (3) cover the stone and culvert with a couple of layers of heavy filter fabric to form a level porous surface; (4) use sandbags and filter fabric to create shelves and planters (possibly using rubber liner to isolate planters from the pond); and (5) fill the pool with water and stock it with plants and fish. 

Note that there is no liner, and therefore no issue of hydrostatic pressure either between the inside/outside of the pool, or between the rock-filled area and the pond.  The water will fill the pool all the way to the bottom.

I'm aware of the other requirements for a healthy pond system.  The water above the filter fabric "liner" will flow continuously, and I will probably use a biological filtration system.  I just need to know if anyone is aware of a problem with doing a pool conversion the way I have described it (e.g. stagnation of the water at the pool bottom, etc).  Thanks!

Buster Harvey
Northern Virginia

[buster_harvey]

I should note - I am not planning on having koi in this pond, but enough goldfish to keep the pond in balance.  I also do not intend to have rocks above the filter fabric layer - the pond bottom and sides will be filter fabric over the crushed stone below and over the sandbags forming the shelves/planters.

Thanks!
Buster

[kitfoxdrvr]

Buster:

I love the idea!  We would love to see pictures as you proceed!

Please note and do some research on the problems with rock/gravel on the bottom of ponds.  I am one of those that does have a relatively thin layer of gravel (about 4") on the bottom of my pond, but many will preach that it is a "sin"!  The danger is that pockets of waste will gather in oxygen poor areas in the gravel and certain types of bacteria will colonize these areas.  These "anaerobic" bacteria produce waste products that are highly toxic to fish.  Eventually, the bottom of your pool COULD become a very bad, poisonous problem with a thick layer of gravel.

I have seen examples of pools converted to ponds, but all have been bare-bottomed, never with gravel on the bottom.  In fact, your bottom intake could easily be converted to a bottom drain like in a traditional koi pond, which would help keep the pond clean.  Do a search on pool pond conversion and you should find several examples; I know I saw one recently over on www.koiphen.com.

Good luck and let us know how you proceed!

Steve

[jw]

Someone else here did that also to a swimming pool and hopefully they will chime in here  . I haven't got a clue but I would love to see how you do it and take pics and post for us to see the progress  . I myself would never do that to my pool if I ever had one...............but that's cause I want one soooooooooooooooooo bad but my DH says no way here in Western Washington  :'(. Good luck on your pool pond 

[Johns]

Buster,

Just my opinion, but as a ponder with 35 years of ponding I would expect your pool as I understand your plans would be a maintenance nightmare.  I may have misunderstood, but it appears as though you intend to create a filter within the pool and use the swimming pool plumbing and filter system to keep the water clear.  I doubt you will be happy with this arrangement, as swimming pool filters do not work well with bio loads.  Your idea of the vertical culvert is ok but I feel that you would be better off to use soil instead of crushed stone which would eliminate the problem of anerobic bacteria in the space below.  If I was doing this project, with the stated desire to maintain the ability to revert back to a swimming pool later on, I would drain and dry out the pool, paint it black, refill and install appropriate pump and bio filter system using the existing pool drains and use plant stands for plants and stock it with fish, sarassa comets if you don't want koi.  Your maintenance chores would be much reduced, your fish would be happier, and reconversion to a swimming pool in the future would be much much easier. 

Just my free, worth what you pay opinion.

[reddad35]

I like your stand pipe idea but I would seal it. This can be removed later. I also would line it and seal attach it to the sides below your outflows and into your standpipe. I would fill it with sand. You should also create a new filter system and leave the pool system be. (just cutting the pipes and reattaching you new system. Might add a pump.  Your other option is to use plant stands and leave the actual pond as is. Just bypass the pool filter system for an inproved pond filter system. This can all be done at the pool filter source. If you want to add a rock feature then run a single pipe but increase water flow. A pool has less filtration than what a pond would need. Good luck.

[buster_harvey]

Hi again folks!

It's busy season here at home, with improvement projects inside and out.  I never know when these fits of motivation are going to arise, but I try to make the most of them when they happen.   

Thanks for your input so far - as a complete pond newbie it's really helpful.

I think I probably didn't explain myself as well as I would have liked to above.  My inspiration is Erik Kilk's pool conversion at -  http://kilk.com/pond/  - but with some significant differences due to building my pond within an intact pool.

I just want to fill the swimming pool up to "pond depth" (about 30 inches) in such a way that (a) I don't get cracks in the pool walls from external hydrostatic pressure, and (b) I don't get hydrostatic "heaving" from below whatever I use for a liner (i.e. water pushing up from below the liner).  Normally, to avoid this second issue, you knock holes in the pool wall, but I don't want to do that.  It really doesn't matter to me whether the fill is dirt or stone, as long as it will accomplish both (a) and (b) above.  In fact, soil would be less expensive, so if it avoids anaerobic bacteria issues I'm all for it.  Likewise, I'm fine with using a regular liner rather than filter cloth, so long as it all works together.  The 30 inch depth is important, as I don't want to have a fence around the pond.

I'm not looking to use the "fill layer" as filtration, or to use the pool plumbing to recycle or filter the pond.  I'll use regular pond-grade pumps and filtration.  The whole idea of keeping the pool drain clear with the stand pipe is so I can control water buildup within the pool (but below my pond) by occasionally draining the area below the pond (especially before draining the pond itself).

So I guess a better way of phrasing my original question is this - if you wanted to preserve an existing pool and convert it to a 30-inch deep pond without knocking holes in the bottom, what do you think would be the best way to do it?

Thanks in advance!

Buster
Northern Virginia