I have a 275 gallon galvanized stock tank that I've used for the last 5 years as a water feature. This past winter, I decided I wanted to convert it into a small goldfish pond and build a bog filter for it.
Recommendations for the size of a bog filter run from 10 to 20% of the total capacity of the pond, so I bought this http://www.amazon.com/Laguna-Plastic-Heavy-Rectangular-60-Gallon/dp/B0074HR8RK/ref=cm_cr_pr_product_top which can be used as a pond. The bin comes pre-drilled with a hole on the short side toward the top, which I cannot imagine a use for. Fortunately, they also send you a plug for it.
Since my tank is 2 feet deep, the bin sits on two courses of concrete block set on 2 inch thick pavers to elevate it high enough for outflow to the tank.
I used 1/2 inch PVC to make a rack to hold my filter media out of the yucky water in the bottom of the bog. We used 4 side outlet elbows and six Ts.
(The blue handled tool at far right is a pair of PVC cutters, and my son highly recommends that you use them.)
He drilled two holes where we wanted them - one for the dump valve on the back, and the other for outflow to the pond. We used 1 inch PVC to make the plumbing for the inflow, and attached 90 degree elbows to the ends, so the water would be forced to circulate toward the corners of the bin.
Since the tubing coming from the pump is 1/2 inch tubing and we are using 1 inch PVC, I needed a reducer to attach the tubing to.
A funny thing happens to me - and I suspect a lot of other women - when we start wandering around a plumbing department in a hardware or big box store. The guy running the department can't believe we really know what we want, and why.
He listened and after I practically diagrammed out my plan, he started digging around in bins, talking to me as he was bringing me fitting after fitting. While he was chattering, I got down on my knees and found a single fitting I thought would replace his 5 or 6, as long as I capped it on the end.
In this shot, you can also see what I call the dump valve, which I'll use to flush the gunk out of the bottom of the bog filter. We used 1 inch PVC with a 1 inch ball valve, to install in the hole drilled on the back of the bin.
The ball valve and the end cap on the reducer are the only two plumbing assemblies that are glued. All winter long, I've haunted pond forums, and one thing I read over and over is how people wished they had not glued all their PVC fittings to the pipe. It seems that no matter how well conceived the design, something always needs to be taken apart - even if it's just to clear a clog.
Uniseals have to be some of the neatest inventions since sliced bread.
They weren't nearly as hard to install as what I had read, but I do recommend using some silicone pipe lube to get the PVC through the seal. The seals are rubber and I did not, as the plumbing guy at Lowes suggested, use WD40 to lubricate them. He's not the one who will have a hellacious mess and a bunch of dead fish on his hands when the seals fail due to deterioration from using a petroleum based product...
For my base filter media, I used the coarsest grade of Matala.
One sheet of it fit nicely in the bin, after cutting about an inch and a half off of it, and slitting an X in the middle for the intake pipe from the pump.
We then attached our 1 inch intake pipe to the pipe running down to our swirlers using one T.
Then it was time for the coarse river rock. I did not want to put the pea gravel directly on top of the Matala, because it was small enough to clog the holes in the Matala. We put the pea gravel on top of the river rock.
I bought http://www.amazon.com/Danner-02527-Pondmaster-700-Pump/dp/B000BJK3QQ/ref=cm_cr_pr_product_top which comes with a plastic pre-filter basket. I bought an extra pre-filter basket in case of problems down the line.
The 1/2 inch tubing connects to the reducer. We installed a 1 1/2 inch outflow pipe from the bog back into the tank. We used some of that inch and a half of extra matala to stuff into the outflow pipe to catch extra trash. I can use an extra 1 1/2 elbow (in the photo below) to control the depth of the water in the bog before it dumps into the tank, if needed. Since it's not glued, I can take it off if I want to.
We backwashed our river rock and gravel through the dump valve for about an hour. Even then, we had some cloudiness in the tank, but all the plumbing works.
I turned the pump off to see if the cloudiness (which is dirt and dust from the rocks) settled without any additional flushing. There was some improvement, but I still wound up flushing the bog filter some more the next morning.
Pond and bog plants were ordered, and I asked for delivery the week of 4/22. The college kids pulling and packing orders ignored that, so my plants will be delivered today in the middle of a major storm, and looking at two nights of lows in the mid to upper 30s. Picture me, unhappily surrounded by various buckets of bare root bog and pond plants in my kitchen.
After I plant, I'll post more pics. I'll wait a week before the first two fish go in.