Up flow vs down flow bog filtration?

[pecan]

I have noticed all instructions out there about natural swimming ponds have a down flow filtration through the bog filter. The pump is housed below the bog rocks pulling the water down through the plants and gravel and pumping it back into the open swimming area.

While all the garden pond bogs I have seen have an up flow filtration through the bog. The pump is in the open water area pumping water to perforated PVC under the plants pushing the water to the bog rather than reversed. I would think up flow would provide better filtration.

Curious what your thoughts are?

 

[Lisak1]

It's an interesting question! I would think pulling water would cause the bog to act like a skimmer, which could cause issues with the bog getting filled with debris on top. Most pond bogs have a pre-filter so the bog isn't dealing with large debris. I guess you could have a separate skimmer, too, but you would still pull stuff to the bog unless you were really diligent about keeping it free of leaves and what not. Just my first thought...

 

[Meyer Jordan]

It's an interesting question! I would think pulling water would cause the bog to act like a skimmer, which could cause issues with the bog getting filled with debris on top. Most pond bogs have a pre-filter so the bog isn't dealing with large debris. I guess you could have a separate skimmer, too, but you would still pull stuff to the bog unless you were really diligent about keeping it free of leaves and what not. Just my first thought...

Yep! What she said.
And I might add, most of what you have read is probably DIY projects. The natural swimming ponds installed by real professionals all have upflow regeneration areas ('bogs')

 

[addy1]

I had a down flow tiny bog and a up flow tiny bog, on the same small pond. The down flow was a pita always getting a layer of yuck covering the top which = clogging and overflow.

 

[Usman]

in the 1st model i see 2 advantages that only filtered water will reach the pump , water will b driven down by gravity and water pressure , pump doesnot need to do much means more volume is being circulated and u can run waterfall from same pump , ihv similar setup

on other hand upflow , pump is sucking all the debris 1st in to it if u dont have pre filter and pump have have to resist water pressure to pump water under the bog thru pipes

 

[Meyer Jordan]

in the 1st model i see 2 advantages that only filtered water will reach the pump , water will b driven down by gravity and water pressure , pump doesnot need to do much

The basic flaw in this design of placing the pump after the 'bog' is when (not if, because it will happen) the 'bog' begins to clog with organic matter the pump will begin to cavitate and this will unnecessarily shorten the life of the pump. In a natural swimming pond (the subject of this thread) full and efficient circulation of the water within the regeneration area ('bog') is critical to maintaining any level of water quality fit for human immersion. More than this regeneration zone is needed however to assure the proper and adequate level of disinfection. In other words, this water must be potable or it is not safe.

 

[pecan]

The basic flaw in this design of placing the pump after the 'bog' is when (not if, because it will happen) the 'bog' begins to clog with organic matter the pump will begin to cavitate and this will unnecessarily shorten the life of the pump. In a natural swimming pond (the subject of this thread) full and efficient circulation of the water within the regeneration area ('bog') is critical to maintaining any level of water quality fit for human immersion. More than this regeneration zone is needed however to assure the proper and adequate level of disinfection. In other words, this water must be potable or it is not safe.

I am not necessarily talking about the best method for a swimming pond but mainly why a person would do one vs the other. Which would provide better filtration? Sounds like up flow is. But I'll note have swam in many bodies of water that were far from potable without any problems and will likely continue to do so.

 

[Meyer Jordan]

For any filtration whether mechanical, biological or Phyto, water movement (in any direction) is an absolute requirement, That being said, it must then be determined which direction of flow will be the most economical and require the least maintenance in a pond application.

Taking these factors into consideration, upflow becomes the obvious choice, mainly because of two (2) factors.

First, as already mentioned, downflow will result in the accumulation of organic debris and algae growth on the surface of the filter, This will severely obstruct any evenly distributed water flow and may result in accumulation of water causing an overflow.
Secondly, when properly constructed, an upflow configuration creates the conditions favorable for any TSS (Total Suspended Solids) to precipitate out as would happen in a dedicated settling tank.

 

[budgenator]

Anybody that has been ponding a while knows things tend to clog, if there is a pump pulling water from the bottom of a bog, and when the bog gets clogged, the pump sucks air and burns out and you have to buy a new one. If the pump is pushing up from the pond to the bottom of the bog, when the bog clogs up, the water runs out the overflow you put in because in ponding things tend to clog, and your pump is Okay.

 

[Boscovius]

Valuable information. I am planning a natural swim pool and I was skeptical of the downflow bog for the stated reasons. I intend to use a bubble lift pump to take detritus laden water from the deepest point in my pool and dump it into an intermediate basin that will screen out the solids via a sheet filter media and gravel. This intermediate basin, like a plastic duck pond, should be the main maintenance concern. Non-perforated flexible drainage tile will take the screened water from outlets at the bottom of the basin and deliver it via gravity feed to perforated drainage tile embedded in coarse gravel and small stones at the bottom of the bog. Water will move upwards through increasingly smaller substrate until it flows through the surface and returns to the pool. To run on 60 watt air compressor.

 

[Mmathis]

@Boscovius Old thread here. Why not go over to our “introductions“ topic and tell us about yourself.

 

[Jhn]

Valuable information. I am planning a natural swim pool and I was skeptical of the downflow bog for the stated reasons. I intend to use a bubble lift pump to take detritus laden water from the deepest point in my pool and dump it into an intermediate basin that will screen out the solids via a sheet filter media and gravel. This intermediate basin, like a plastic duck pond, should be the main maintenance concern. Non-perforated flexible drainage tile will take the screened water from outlets at the bottom of the basin and deliver it via gravity feed to perforated drainage tile embedded in coarse gravel and small stones at the bottom of the bog. Water will move upwards through increasingly smaller substrate until it flows through the surface and returns to the pool. To run on 60 watt air compressor.

You could do away with the gravel and sheet filter in your settling tank/intermediate basin, and just raise the inlets and outlets off the bottom. This will let any solids settle out before heading towards the bog/regeneration zone of your pond. Then can drain and clean settling tank as needed. Less filter rinsing and much less chance of clogging and overflowing the top of the basin.