Wednesday, April 7, 2010

How I Keep My Pond Water Crystal Clear

As I was doing spring maintenance on our backyard pond today I saw the opportunity to pass on what I've learned about keeping pond water clear. Many people have asked me how I do it, especially people who have ponds. The fact is that it wasn't a simple step but a long process of trial and improvements to reach a simple method. I want to save you all that time and effort and tell you what I've learned. For those of you thinking "Just get to the end Dutch!", the secret is rocks. OK there you have it. Now I will get to the long explanation.
If you are seeking ways to keep your pond clear then it must be either cloudy or, most likely, opaque green. That is the condition I want to address the green water is a result of algae blooms. Cloudy water could have several causes but the rocks will help a great deal with those too. Algae blooms are a result of temperature and sunlight. If you live in a climate with cold winters you will not see the algae during winter. Algae needs warm temperatures to survive. Sunlight is the power behind photosynthesis and the green color is a giveaway that photosynthesis is going on. Plants use photosynthesis for energy to grow, breathe, pump water and all the stuff green plants do. Algae is a green plant that is in the air and consequently ends up in your pond. Once the conditions are right it will bloom and coat all the surfaces with a slimy green coat, and turn your water to pea soup.

Ignore the hype
Skip all the marketing hype out there. People will try to sell you chemicals, UV lamps, floating plants, pieces of copper and all kinds of other stuff that mostly makes them money, your money. There are probably a bunch of their ads in the margins of this blog. The chemicals are not a good idea for pond life no matter what the label claims. Even if you don't care about pond life and essentially want an ornamental pond full of swimming pool water you will have to buy chemicals constantly. UV lamps work but they carry a hefty price tag and ongoing electric consumption. Also you are once again killing more than just algae. Adding just the right amount of copper to hurt the algae but not your pond life is a balancing act that I put in the same category as chemicals. Floating plants or other methods of shading the pond to reduce sunlight and slow photosynthesis does what it says. The trouble is that the plants end up covering the entire pond surface so you still can't see your fish in there and chances are you still have algae anyway.

Biological critters
The most effective and sensible approach is a biological filter. That is a filter that uses biological organisms that compete with the algae for food and also break down organic waste that causes cloudiness. The biological critters we want to grow are bacteria. These bacteria do not eat algae, they eat what the algae eats. Once they start growing they will increase to a level where they use up the nutrients needed by the algae and the algae bloom will die. The bacteria will reach a critical mass that balances the available nutrients with the population of bacteria. The only side effects of this bacteria colony are clear water, and a brown coating on hard surfaces in the pond that does not hurt the aesthetics of the pond or it's eco-system.
How do we cultivate this benefical bacteria? Well it needs a few things to grow which we have to provide. Moving water is extremely important as are surfaces for the bacteria to grow on.
The moving water is provided by a pump. You will need to purchase a pump that is strong enough to pump the water from the lowest point in your pond to the highest point, which will be the biological filter inlet, and provide a relatively strong moving current throughout the pond system. This has to be a "solids handling" pump. That is a pump that will not get clogged with dirt and other water contaminants but pump them from the bottom of your pond system to the filter where they can collect.

You gotta rock!
The surface area is provided by rocks. Rocks with bumps, crannies, pores etc. The more convoluted the rocks the more surface area. Also the beneficial bacteria loves to live in little crevices.
Now there are vendors out there that will sell you all sorts of biological filters with all sorts of filter mediums. Plastic with holes in it, charcoal medium, etc. They will tell you that their filter medium is the best and it's been researched and tested blah blah. The fact is you have to buy it, and guess what? The guy telling you how great it is happens to sell it too. In my quest for clear water I tried many many mediums for the biological filer and the best medium I have found is also the cheapest; rocks. That's what works in natural streams and that is what works in moving pond water. Plastic does not work no matter how many holes are in it. I've tried hair curlers, army men, plastic building blocks, furnace filter material, (this blue stuff does not work at all save your time and effort. It seems like it would be great but it is not), women's hair pieces, rope, and many other things that seemed feasible as a bacteria habitat. Rocks win out over all others as the most effective, cheapest, easiest to maintain biological filter medium. This is no big secret, there are many others offering the same advice as me about using rocks, I'm just telling you to listen to them, don't waste time, get right to the rocks.
Now that I've sold you on rocks, how do we get them to become a pond filter? I'll show you how I make mine and you can do that or use the basic principle to build one that suits you. Basically you must pump the dirty water from the low part of the pond system through the rocks and keep it moving.

How to build it
I first started with a rubber tote box full of rocks and I perked the water up through the bottom of this and out the top into the top of my pond system. I got the plans from the internet somewhere, like I said there are others out there telling you to use rocks and how. My pond system consists of three pre-cast pond liners with cascading waterfalls between them. The top one is the smallest and after a while I decided to just make that into the biological filter and eliminate the box.
The trick is to get the water to percolate up through the rocks from the bottom. To do this I stood a PVC pipe in the middle of the rocks with holes in the bottom to push the water up from the bottom. Here is a picture of the inlet pipe with my pile of rocks. Notice the notches and holes at the bottom end to deliver the dirty water to the bottom of the filter.
I use a rectangle of PVC pipe that sits a few inches above the bottom of the filter vessel to stabilize the vertical feeder pipe. Mine came from a previous version of the filter so it has different fittings on it.
The idea is to create a space at the bottom of the filter below the rocks for the incoming water to churn and debris to collect. I put pieces of ceiling light grid material on it to hold the rocks up off the bottom. Fit this shelf to the container or prop it up off the bottom with a few good old rocks.

Now just fill the top with rocks up to a level that will be a few inches below the water surface when full. It's prettier that way. Use common sense when filling in the rocks. A lot of small rocks are better than fewer large ones. We are going for maximum surface area here. Mine are mostly granite because that is what is in the ground in my yard. I use larger rocks to plug the gaps in the plastic grate I use for a shelf. That way the smaller ones do not fall through. We want to preserve that open space below the rock bed. Pile a lot of smaller rocks around the feeder pipe, this is where the strongest up-current of water will be. You want to slow down the water and make it pass over as much rock surface as possible before reaching the top. I also have some large flat rocks next to the inlet pipe that provide a support for an iron pump I use to make the inlet pipe more decorative. You will notice that there is dirt included with the rocks, that will not hurt and actually will help get the bacteria started.
All that remains is to stick the outlet tube from your circulating pump down into the feeder tube and put a rock in there or something to prevent it from popping out.
I added an iron pump and a little bucket around the feeder tube to dress up the aesthetics then I just fed the circulating pump hose in through the bottom of the iron pump. Turn on the pump and the water should go down the feeder tube and out through the holes and notches forcing it up through the rocks. From there it enters your pond system.
To get the bacteria going purchase a bottle of biological filter bacteria at a pond supply store. This stinky stuff is expensive, expect to pay upwards of $20 for a bottle. If you do it correctly you will only have to buy it once and it is worth the money to get the initial jump-start working. Follow the directions and add a little every few days and watch your water for results.
Never turn your circulating pump off, it must run 24/7 for the bacteria to work. After some time the green water will turn brown, this is the algae dying. If you have any ornamental fountains or spitters with foam filters on them you may want to disable them until the water clears or they will clog every few minutes with the dead algae. Once the algae dies it is only a matter of a day or so before it all collects in the bottom of your biological filter and the pond becomes crystal clear.
You will see dark slime form on hard surfaces in your pond and especially the waterfalls this is the bacteria colony. The bacteria slime feels tacky not slippery. put your hand in the water and when you remove it and rub your fingers together it should not feel slippery but rather tacky. Then you know the beneficial bacteria is growing.

How to maintain it
To maintain your new bacterial eco-system keep the water moving at all times. I keep my pump running through winter and use a pond heater to prevent solid freeze overs. Then in spring preferably before the first algae bloom remove all the rocks and water from the filter then brush inside of the filter and rinse the rocks using only plain pond water. Replace the rocks and you are good for another year. This is to remove toxic buildup from the bottom of the filter that will make it uncomfortable for your pond life and also stink. I pour the dirty filter water in the garden it is high nitrogen fertilizer. Here is a good place to mention planting the rock bed with water plants. The theory that the plants will consume and thrive on the toxins is a sound one. I tried it and the failure point was that the plants thrived so well that thier roots filled the entire rock bed and the filtration process broke down. So take that vicarious experience for what it is worth.
This maintenance procedure keeps my pond's bacteria colony alive and I never have to buy the expensive stinky-stuff to jump-start it anymore. If your colony dies over winter or from a stop of water flow you can start a new one with the bottled bacteria, or if you are patient enough just run the filter, put a handful of dirt in and the bacteria will grow naturally although much slower at first. The bacteria will overpower algae blooms and break down fish waste and other organic pollutants forever by using the same rocks if you do this simple maintenance. Cheap, re-use-able, effective, ROCKS.

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  1. I agree with your rock method? I changed my system to use lava rocks and with ladies silk stocking. packed with the lava rock and using 950gph pump and plastic bin with the sides open and flow the water over a slate.Making it look like a falls.

    The small holes in the lava rocks fill-up with the dirt and etc and clean once a year with fresh
    water and restart again its been two years now and it works.the water does have some green but not clear as the water in your photo. Next year I will try your method and idea.


  2. That's fantastic to read and has inspired me to give it a go myself. I have had nothing but trouble with coloured water and my filtration system isn't amazing. I have currently got two pressurised filters running, one 12,000 litre with 13W UVC and another 10,000 litre with 11W UVC. This has cost me a bomb and should hopefully help my pond for the mechanical filtration side and a bit of the green in late spring and through summer when the sun shines.

    However, I have a decking installed behind the pond with a bridge over the pond. I am thinking that I might make a 3 metre x 1m x 1m box out of decking, line this with pond liner and fill it with gravel/pebbles. I will try running 1200 gph through it to not only keep the water clear but also to help the fish to thrive!

    Thanks for your help!

  3. I think this article explains what we have stumbled into this year. Previous years we tried to keep a sterile pond using chemicals and always lost to algae. This year we went with purchased bacteria (Pond Clear) and no other chemicals. After about a month we started to get brown on our rocks and were getting worried. But today I sampled the water and it is crystal clear. Our pond is only 30 inches deep with rocks over a liner. The circulation is good, the whole water turns over every 90 minutes with a waterfall, jets and a spray fountain. With the shallow depth and clear water the brown on the rocks makes the whole pond look like tea. Now I just have to convince everyone it is a "good thing". Probably much better to have rocks in a confined filter not so visible. Maybe future plan. But we are talking about a 27,000 gallon pool.