Question About Raised Bog Maintenance


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Hi Everyone,

Just over a year ago I constructed a 300 gallon buried stock tank pond with a slightly raised bog filter approximately 24% the area of the pond and a small waterfall (https://www.gardenpondforum.com/threads/first-pond-taking-shape.28098/). This forum was extremely helpful - thank you again for all your expertise and advice!

Overall, everything has been going really well. The water stays remarkably clear and all the plants seem very happy and they really take off in summer. Lately, however, I've noticed that the waterfall coming out of the raised bog has slowed down and its flow is about 1/2 - 3/4 of what it was before. I unscrewed the maintenance cap and flushed the system and it flowed very freely, which to me suggests there is not a major clog in the pipes. I also cleaned off the bottom of the pond a bit and cleaned the pump itself. I'm wondering if the array of pipes at the very bottom of the bog underneath all the gravel - the ones with small holes drilled in them to release the water from the bottom up - are becoming clogged with algae and muck. This is a pretty small setup compared to what a lot of people here have, so it is probably more prone to that kind of build-up.

Is this something other people have experienced with the bog filters over time? Is it necessary to periodically empty the bog of the gravel and plants and clean it out?
 
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brokensword

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what I've found is that as the summer matures, the plants and their roots clog up available space where the water once flowed. A couple of things can happen then; the water will channel and find its way up along the sides of the bog liner and you'll get more water on top of the gravel, which doesn't affect what you see as your outlet flow. But, if that avenue is also clogged, the water from the pump gets back pressure and you don't get full bog effect. Another aspect, which hopefully you don't have, is that the bog gravel itself is indeed clogging down below. Most of the designs here at GPF advocate cutting SLITS not holes in your manifold. If you did holes, that too can more easily clog and any algae like substance might not get flushed from the actual hole perimeter, thus reducing your flow. Probably too late to cut slits (though, if you ever get the chance, replace the holes with slits cut 1/3 the way through your manifold). Have you thinned the plants in your bog? And by this, I mean yanking and taking the plants out including the roots? This would also help water flow.

It is possible your gravel IS getting clogged from below simply because you're forcing too much water(and larger debris) through and it's taking too long for any larger debris to break down, necessitating an actual gravel cleaning. Not sure how much(depth) you have, but it might work to your advantage to (I'd do it in the spring or late fall) actually dig everything up and clean it out. IF you installed a snorkel/pump vault, then you'd clean that way. If not, you'd have to actually dig, wash, put back (and if you DO do this, consider the slits/manifold problem fix).

Now, if you DO have a pump vault built into your bog system, this is the method of backflushing/washing the bog. You'll need a pump like your pond pump (something that pushes a lot of water forcefully--NOT house pressure and a hose--ask me how I know this!) and with the pump's lead, push water from the top of your bog to wash back through the gravel. This forces any blockage at the base of your gravel to break free. You SHOULD have dug your bog such that it drains naturally to one point lower than the rest. Your pump vault should be here. You take another pump and lower it down into the vault and then pump out the backflushed water until it goes clear. Typically, should take 2-3 backflushes/pumpouts to get to this point. If you're going to do this, I'd dig all the plants out and make it easier on yourself; you can then replant them when you're done. That's why I 'd do it in early spring or late fall, before/after plant activity has started/stopped.
 
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In the beginning I was flushing mine more often. Usually when the return water slowed down as you have stated.

The function of the bog is to keep the water clear and healthy. I've come to realize that as long as it is doing it's job, why mess with it so often?

There have been discussions on the speed of turnover of the bog water.
How fast or slow should it be?
Is slower better?
How slow?
Can it be too slow? I really don't think so.

Now I just let it be for a lot longer and the water is still crystal clear.
I think it would work fine if I did nothing.

One point I'll make is not to have your pump intake on the very bottom of your pond. Keep it suspended with a string so that it doesn't suck up any solid debris that may collect on the bottom. You dont really want any solids clogging up your bog.
Use a net to slowly comb the bottom for leaves, sticks, acorns, etc.
 
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Thanks so much for the replies! I realized I misremembered / mistyped earlier. We did indeed cut slits into the pipes at the bottom of the bog, rather than drilling holes. The plants in the bog have certainly grown, but not to the point of overcrowding; they will likely benefit from some thinning at some point, however. Yes, I have the pump elevated off of the bottom of the pond, and I cleared the bottom of all major debris.

Since the bog is still flowing nicely, albeit not as fast as before, and the water is strikingly clear, I think I'll leave it for now and keep monitoring. If anyone else has experiences or advice to share on this matter, I'd love to hear them!
 

brokensword

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Thanks so much for the replies! I realized I misremembered / mistyped earlier. We did indeed cut slits into the pipes at the bottom of the bog, rather than drilling holes. The plants in the bog have certainly grown, but not to the point of overcrowding; they will likely benefit from some thinning at some point, however. Yes, I have the pump elevated off of the bottom of the pond, and I cleared the bottom of all major debris.

Since the bog is still flowing nicely, albeit not as fast as before, and the water is strikingly clear, I think I'll leave it for now and keep monitoring. If anyone else has experiences or advice to share on this matter, I'd love to hear them!
You can also check to see your pump isn't being restricted by debris or whatnot. The impeller area can also get gummed up and slow your roll. You can try and experiment and yank a part of your bog, noting ALL the roots of that particular piece come with the stem. And doing this in a few places (thinning), you might see a better rush of water. Too, poke at the gravel and see how much 'dirt/debris' is visible; might be a buildup there and some 'end of season' cleaning would help. The hope is the debris/dirt decomposes as fast or faster than it accumulates. I've gone to a bog prefilter and am surprised the quantity of small particles I'm getting.
 

addy1

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My bog just gets plant yanking done to it for maintenance. Never see a slow down but mine is huge I send a lot of water through it.
 
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brokensword

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My bog just gets plant yanking done to it for maintenance. Never see a slow down but mine is huge I send a lot of water through it.
so, there you go; addy's suggestion is to DABB it (dig a bigger bog)

( @addy1 are ya getting this one down for the acro list???)
 
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