GPH for Bog Filter..?

[Mucky_Waters]

"suggested retention time should be greater than 24 hrs."

Well, if that's the case then I'm pretty sure that no backyard pond owners are achieving anywhere close to the "suggested retention time" in their bogs, except on those rare occasions when they happen to experience a 24 hour power outage.

 

[Stephen T.]

I would think that things are totally different in a catch/process/release environment with a one time pass through. The recirculating of a pond/bog filter sytem means that the same water is slowly flowing through the bog over and over. I'm sure it shouldn't "blast through", but a steady slow flow should work as a continuous nutrient feed to the bog. I could be totally wrong about this, but it seems like this is the way it would work.

 

[Meyer Jordan]

Well, if that's the case then I'm pretty sure that no backyard pond owners are achieving anywhere close to the "suggested retention time" in their bogs, except on those rare occasions when they happen to experience a 24 hour power outage.

And you are most likely correct as many pond keepers are using "bog" filters as the primary filter which is fine. However this is not the most efficient use of this type of filtration system.

I'm sure it shouldn't "blast through", but a steady slow flow should work as a continuous nutrient feed to the bog.

Exactly. Only the issue of what constitutes "blast through" and "steady flow" needs to be determined.

 

[Meyer Jordan]

The recirculating of a pond/bog filter sytem means that the same water is slowly flowing through the bog over and over.

This is not exactly the "same water" as Nitrate and other pollutants are being constantly added to the water column of a recirculating pond. The "bog" should have the ability to remove more pollutants than is being produced.

 

[Stephen T.]

So another aspect will be the density of plants in the bog and how "hungry" the specific plants are. I assume that faster growing plants will use more nutrients. Temperature of both air and water are also likely to have a major affect on nutrient absorption.

Since each pond and the variables will be different, a large, heavily planted bog to pond size ratio is the surest bet. (I guess).

 

[Mucky_Waters]

The "bog" should have the ability to remove more pollutants than is being produced.

Lets forget about (one time pass) wetland filters and just focus on (recirculating) bogs for backyard ponds.
It's pretty obvious there is no established recommended ratio for bog size to dwell time (flow rate) like there is with settling chambers. That being the case it's kind of hard to say with any authority what the dwell time should be, especially with all the other variables. All we can do is guess what a proper dwell time might be.

Since each pond and the variables will be different, a large, heavily planted bog to pond size ratio is the surest bet. (I guess).

Exactly

 

[Meyer Jordan]

Here is a chart of one constructed wetlands filter with variable flow rates and how this affected nutrient uptake by the plants.
One can easily see that the lower the flow rate the better the nutrient assimilation by the plants.

As each pond is different, so will "bog" filters. Size, sub-strate, type (species) of plants and planting density all, of course play a part, but transport of nutrients to the plants and available time for assimilation is the limiting factor on a 'bog's" efficiency.
The lower the flow rate the greater the nutrient uptake. Aim for the lowest flow rate that is practical for a particular.
Referring back to the OP's system, Reducing the flow rate any amount from the 800 gph will improve the "bog's" efficiency. The more it is reduced the greater the efficiency. It is that simple.

 

[Mucky_Waters]

Meyers those charts aren't relevant to a recirculating system. In the kind of wetland filter they apply to the plants have only one shot at absorbing nutrients, etc,,, from the water before it gets introduced back into other bodies of water like streams, or lakes. So yes, dwell time is crucial to giving the plants the best chance of absorbing as much as they can with that one shot.
In a backyard pond recirculating system however, the plants have endless shots at absorbing the nutrients from the same water. In that regard it could be argued that a faster flow rate may be desired so the plants can get more chances of absorbing the nutrients they missed the last time they flowed through. So no, it's not quite that simple.

 

[Meyer Jordan]

Meyers those charts aren't relevant to a recirculating system. In the kind of wetland filter they apply to the plants have only one shot at absorbing nutrients, etc,,, from the water before it gets introduced back into other bodies of water like streams, or lakes. So yes, dwell time is crucial to giving the plants the best chance of absorbing as much as they can with that one shot.
In a backyard pond recirculating system however, the plants have endless shots at absorbing the nutrients from the same water. In that regard it could be argued that a faster flow rate may be desired so the plants can get more chances of absorbing the nutrients they missed the last time they flowed through. So no, it's not quite that simple.

All that may be true, but Nutrients and pollutants are constantly being added to a pond's water column. This is especially true in a pond with a high fish load.
The lower flow rate applies no matter whether it is a flow through or re-circulating system. I have seen the results first-hand.
And the chart shows the difference in plant uptake of nutrients as the flow rate changes. This nutrient assimilation rate is constant for plants regardless of type of system.

 

[Mucky_Waters]

Another thing to consider, that relates back to that of a settling tank concept, is possible adverse effect of too slow a dwell time in a bog would encourage the settling of solids. I've read of many experiences of people who've had bogs they had to clean out that were deep in stinky anaerobic muck and debris after only a year or two. And yet, I've also heard from people with bogs they've had running for many more years and they've dug into them and found virtually no signs of accumulated solids. My guess is that those who experience the latter likely had the water flowing through their bogs with much shorter dwell times.

 

[Meyer Jordan]

Another thing to consider, that relates back to that of a settling tank concept, is possible adverse effect of too slow a dwell time in a bog would encourage the settling of solids. I've read of many experiences of people who've had bogs they had to clean out that were deep in stinky anaerobic muck and debris after only a year or two. And yet, I've also heard from people with bogs they've had running for many more years and they've dug into them and found virtually no signs of accumulated solids. My guess is that those who experience the latter likely had the water flowing through their bogs with much shorter dwell times.

Actually the opposite is more likely. Due to the small void space with pea gravel (which is the usual sub-strate of choice), solids will accumulate faster than bacterial action can break them down in a high flow rate bog much like a biofilter will accumulate the same organic matter and require cleaning or back-flushing. This is another reason that sufficient dwell or resident time in a wetlands filter is important. This clogging is especially troublesome in "bogs" that are not prefaced by mechanical filtration and in ponds that experience a heavier than normal deposit of external organic matter.

 

[addy1]

Mine gets minimal debris, I have two good leaf baskets that collect any large matter. Maybe that is why is is still doing fine. I also don't draw from the bottom of the pond. I draw the water mid level. Large debris that manages to collect on the bottom which is minimal, gets netted out once a year. Or when I think of it.

 

[Mucky_Waters]

It goes without saying that the better you pre-filter the water going into a bog the less solids you'll have available to settle in there, and I will concede that higher flows will mean more water (and more solids) will pass through per given time period, and with more solids per hour entering the bog there is more chance for those solids to accumulate, but it's pretty common knowledge that slower water flows (longer dwell times) promote solids settling.
However I'll give this one to you, not because of the bacteria action having time to break down the solids. but on second thought I realized likely the pea gravel screening and filtering effect would have more influence on trapping the debris then faster flowing water could overcome. You win

 

[Meyer Jordan]

You win

No, science wins. All I did was relay information.

 

[Meyer Jordan]

Mine gets minimal debris, I have two good leaf baskets that collect any large matter. Maybe that is why is is still doing fine. I also don't draw from the bottom of the pond. I draw the water mid level. Large debris that manages to collect on the bottom which is minimal, gets netted out once a year. Or when I think of it.

How often is it necessary to empty these leaf baskets during leaf drop season (Fall)?