Can this simple ecological filter keep our pool clean? We’re going to find out!

A bog filter (also known as a wetland filter) uses a bed of gravel and plants to filter and clean water. As the water is pumped through the bottom of the gravel bed, it flows up towards the drain, through the gravel. Nitrifying bacteria on the gravel break down and convert nutrients into plant available form, which the plants in the filter then take up to use for growth.

We stopped chlorinating our pool in 2020. We were doing all the maintenance and hated the expense, handling chemicals and swimming in the chlorine, so we just stopped. We also disliked that the water wasn’t useful to wildlife.

We left it alone for well over a year. It got pretty gross, but it did grow some huge bullfrogs.

We drained it, cleaned it out and sanitized it this winter in preparation for the conversion to a pond that we hope to be able to swim in.

Then we added about 18,000 gallons of fresh water back into it.

I was able to get a good month of cold plunges in before the string algae took over.

I’ve been diligently netting it out, but with warmer weather approaching, the pool was getting greener by the day.

It was time to act fast.

Using this article by Nelson Water Gardens and others as a guide, I got to work building the bog filter.

We begin with an empty 8′ stock tank from tractor supply.

Sealed the gap with clay 🤷

Got tank positioned and added a bottom drain valve. Tape and dope.

Now I can irrigate bananas with pond water!

Cut and dry fit bog filter assembly.

Added an overflow drain to the pool.

3 inch hole saw, 2 inch uniseal. Pro tip: go in reverse for a super clean hole.

Connecting the tank overflow to the pond.

Cutters fell apart on me here.

A random nut in my random bin saved the day.

Glued bottom manifold assembly.

I chamfer my pipes.

Marked out every 1 inch along pipes and cut with circular saw.

A bit of a mess.

Shop vac takes care of it.

Back to the tank.

Levelled it.

Connected the pump. This is a Pro HY-DRIVE 4800. I reckon I’m getting about 2500 gallons per hour.

Flow test. It totally failed.

All the flow was coming out of the end of the middle line. Makes sense.

Yanked it out. Cut it up.

New design. Next time I would try to have an even amount of lines so I could come into the top with a tee rather than a cross. That would break up the flow and distribute it better.

I hope this works.

What a relief! That fix made it to where water flows up mostly evenly through all the holes.

Levelled and started filling with 3/8″ pea gravel.

Had to drive on some mojito mint to pull this off, but I think it was worth it.

That one drain wasn’t enough to keep up with the flow from the pump. So I needed to add a second drain.

Now we have two lines draining back to the pool, it’s awesome!

I’m playing around with 90 degree fittings for adjusting the discharge from the drains. This is all 2 inch schedule 40 PVC.

Ready to plant!

I picked up some Taro (Eddoe) from the grocery store and stuck them in here until some other plants come in. It would be better to have more mature plants ready to go and start absorbing nutrients from the pool.

It will take some time for the bacteria to grow on the gravel, establish themselves and begin breaking down nutrients into plant available forms.

That said, the filter is already fulfilling a critical function: water circulation and oxygenation.

It’s also permeating our outdoor space with the most pleasant sound of running water.

That circulation and oxygenation is critical for the health of fish… perfect timing!

We added 40 mosquito fish and 11 shubunkin goldfish to the pool.

Still waiting on a bunch of pond plants that shipped late. It would be better to have plants for them already but we have added some habitat to the pool so hopefully the fish can make it until then.