Filtration for a 220 gallon outdoor tank

[Orthoducks]

The "pond" in question is a repurposed spa with a capacity of about 220 gallons. It's located behind my house in a climate where we have about a 50/50 chance of getting a hard freeze on the coldest nights each winter.

The spa is home to a couple of small carp and several smaller fish. The water gets very murky in the summer, and there are probably several inches of accumulated muck on the bottom. I want to get a filter that will clean up the water and keep it reasonably clean while I gradually clean out the muck.

I can't find a filter suitable for this application. The smallest pond filters I've seen are rated for about five times the water volume I have, with proportionately large prices and power requirements.

I can get a suitably sized aquarium canister filter, but the ones I've studied have restrictions that make them unusable. For example: do not expose the filter` to weather, do not let it freeze, and position it under the tank with hoses leading directly up to the edge of the tank. The spa has no "under"; I can put a filter on the pavement next to it, but that would maximize its exposure to rain, and might allow it to freeze on the coldest winter nights. Or I can put one on a window sill where it will stay dry and won't freeze, but then it will be a couple of feet away from the spa and a foot above the surface of the water.

Are there any filters that will fit my needs, or any alternative way of cleaning up the water?

Please note: I want to clear out the muck and keep the water reasonably clean; I don't want to keep it clean by aquarium standards. The fish have all survived years of spa life with no cleaning at all, and I'm wary of changing their environment completely. I've read that the carp, at least, like somewhat cloudy water, and I don't want to take away their ability to hide from predators by going down to the bottom.

I've read that an aquarium filter should be able to process the volume of the tank every hour. I don't know how much capacity I need, but I think it's a lot less than that.

 

[j.w]

@Orthoducks

 

[Stephen Noble]

Welcome!
Could you place a small bog filter next to the spa and have it gravity feed the water back into the pond? Given you live in a warmer climate, a bog will perform nearly all year. If you just want to move the water to prevent stagnation, get a couple of pond-size sponge filters and hook 'em up to an outdoor rated air pump. Toss in some floating plants to help suck up the excessive nutrients and away you go. Or find an internal pond filter. Tetra has a flat box 250/500 fountain/filter and Laguna has the 3500. Either or similar should do the job. But do consider a bog first.

 

[Mmathis]

Hello and welcome!

Have you tried any pumps/filters yet?

 

[Orthoducks]

I never heard of a bog filter. Looked it up, it really isn't practical here. The spa is on the patio. I'd have to start by cutting a hole in it with a concrete saw.

I haven't tried any filters yet, I'm just trying to figure out what to try. I ran across the flat filter you mentioned or one like it, but it doesn't seem promising to me either. My plan (not fixed in stone) is to scoop out a little of the muck, let the filter clear the water of whatever muck I disturbed, then repeat, perhaps once a day. If a flat filter is placed on the bottom it will be in the muck, and I think it will either immediately clog, or suck up an overwhelming amount of muck and spew it through the water. One possibility would be bad for the filter, the other bad for the fish.

Maybe I could get a flat filter and suspend it a few inches under the surface, but the systems designer in me is suspicious of plans like that. I'd have to be able to set it up so that the filter was absolutely secure. If it slipped out of place just once it would fall to the bottom and maybe cause a disaster.

I've thought about setting up some kind of aquatic vacuum cleaner that would let me suck some of the muck directly out of the spa, filter it, and return it. Or just let it settle in another container, then return the (relatively) clear water to the spa and dump the muck. I could get a small pump and try that. If I want a filter I'm back with the original problem of how to find one that's adaptable to this situation but not too big and expensive. But if I don't intend to use it permanently, weather at least will no longer matter.

There used to be plants in the spa. They lived several years, but two or three winters back they all died. While they were there they covered the surface so I couldn't see the fish. Maybe I need different plants. But I don't know anything about water plants and don't really want to take the time to learn. My wife got the fish (she passed away last year) and as long as they're here I want to take good care of them, but I don't want to make a big project out of it.

 

[RMaynard]

The bog filter doesn't have to be cut into a hole in your patio. It can be a raised container with about 12" depth, and 1/4 the surface area of your spa. Pump the water up from the bottom of the spa, into the bottom of the bog, and overflow from the bog back into the spa.

 

[Hound Heaven]

I have used these before - put a bulkhead fitting low on the side and run the water in from your pump. Fill it with pea gravel and plants and the water can escape via the spout back to your pond. Instant bog whiskey liner w/spout

 

[Orthoducks]

That could work. The spa is between knee- and waist-height, so I'd have to raise the top of the bog container higher than that. And I'd have to add some kind of extension to its spout. The spa has sides like a bathtub, not a fish tank, and I'd need at least 4" of overhang to let the water fall into the spa and not onto the edge.

It's not clear to me what happens to the muck after I pump it into the bog. It's not little particles that plants can absorb or decompose; it's more like concentrated liquified clay. Maybe I will have to take out the plants out and clean out the bog quite frequently until I get the muck under control. I'll have to read up on that.

How much water flow should I have for something like this? It seems to me that the flow should be small; the water in the bog needs time for the muck to settle out and the plants to do their thing before it flows back again.

I just thought of something: Over ten years ago my wife bought a big hard rubber tank, maybe 50 gallons, at a garage sale. She never did anything with it, and I didn't understand what it was for, but it was probably for something like this, and maybe I could use it now. I'll have a close look at it later today.

 

[GBBUDD]

The "pond" in question is a repurposed spa with a capacity of about 220 gallons. It's located behind my house in a climate where we have about a 50/50 chance of getting a hard freeze on the coldest nights each winter.

The spa is home to a couple of small carp and several smaller fish. The water gets very murky in the summer, and there are probably several inches of accumulated muck on the bottom. I want to get a filter that will clean up the water and keep it reasonably clean while I gradually clean out the muck.

I can't find a filter suitable for this application. The smallest pond filters I've seen are rated for about five times the water volume I have, with proportionately large prices and power requirements.

I can get a suitably sized aquarium canister filter, but the ones I've studied have restrictions that make them unusable. For example: do not expose the filter` to weather, do not let it freeze, and position it under the tank with hoses leading directly up to the edge of the tank. The spa has no "under"; I can put a filter on the pavement next to it, but that would maximize its exposure to rain, and might allow it to freeze on the coldest winter nights. Or I can put one on a window sill where it will stay dry and won't freeze, but then it will be a couple of feet away from the spa and a foot above the surface of the water.

Are there any filters that will fit my needs, or any alternative way of cleaning up the water?

Please note: I want to clear out the muck and keep the water reasonably clean; I don't want to keep it clean by aquarium standards. The fish have all survived years of spa life with no cleaning at all, and I'm wary of changing their environment completely. I've read that the carp, at least, like somewhat cloudy water, and I don't want to take away their ability to hide from predators by going down to the bottom.

I've read that an aquarium filter should be able to process the volume of the tank every hour. I don't know how much capacity I need, but I think it's a lot less than that.

ehiem professional would be my choice for an aquarium pomp that or a green reset from the pond builds or an oase rdf filter a bog is a third option

 

[RMaynard]

That could work. The spa is between knee- and waist-height, so I'd have to raise the top of the bog container higher than that. And I'd have to add some kind of extension to its spout. The spa has sides like a bathtub, not a fish tank, and I'd need at least 4" of overhang to let the water fall into the spa and not onto the edge.

It's not clear to me what happens to the muck after I pump it into the bog. It's not little particles that plants can absorb or decompose; it's more like concentrated liquified clay. Maybe I will have to take out the plants out and clean out the bog quite frequently until I get the muck under control. I'll have to read up on that.

How much water flow should I have for something like this? It seems to me that the flow should be small; the water in the bog needs time for the muck to settle out and the plants to do their thing before it flows back again.

I just thought of something: Over ten years ago my wife bought a big hard rubber tank, maybe 50 gallons, at a garage sale. She never did anything with it, and I didn't understand what it was for, but it was probably for something like this, and maybe I could use it now. I'll have a close look at it later today.

You might try an intermediate container that sits on the edge of the spa and catches the bog water, directing it into the pond..

I would not try to process the existing settled muck through the bog. Use a shop vac to suck as much out as you can.

I would think something around 500gph would be appropriate. Something like this would be reliable and efficient.

I would keep the pump inside a small bucket... it keeps the pump from sucking up muck straight from the bottom (that stuff isn't harmful if it stays settled), and also will prevent the pump from completely emptying the pond if there is some kind of leak in the plumbing or bog.

 

[Orthoducks]

@RMaynard, I'm taking your advice about the muck to heart -- not that I want to leave it there, but I've decided that I shouldn't try to get it out until the water is at least clear enough that I can see the much and be sure what its properties are. Maybe it's mud that I can remove with a scoop, or maybe it's a slurry that I can suck out with a pump.

I dunno about getting it out with a shop vac. I know my shop vac is supposed to be able to handle liquids, but I think that means sucking up little pools of water on a concrete floor... not sucking a layer of muddy water out of a fish habitat. A small external aquarium pump or trash pump sounds more appropriate. Something that attaches to a 1/2" tube.

Your suggestion of a 500 GPH pump puzzles me. The literature I've read says a pump should be able to move the volume of the tank every hour: 220 gph for a 220 gallon tank. I've always felt that for my purpose (to make the water cleaner, but not to keep it crystal clear) that's too big by a factor of three or four. But you're recommending a pump that's over twice as big, instead of 1/4 to 1/3 as big. What is the advantage of using a 500 gph pump instead of 220 gph? What is the problem with using a 50 or 60 gph pump instead of 220 gph, apart from a higher concentration of waste when the water reaches a stable point?