What is the correct way to build a bog filter and are there substitutes for bog filter media?

[ASchell90]

From my research i have come across differing opinions on what is the right and the wrong way to build a bog filter. I am thoroughly confused on the matter and would hope someone would be able to give me a quick rundown of the major pitfalls to avoid and helpful tips.

I have constructed a pond that is 15 feet by 15 with a maximum depth of 7 feet in the center. I have dug down to a layer of thick blue-white clay and I am in the process of shaping the sides. It is a labor intensive process because we live on a hill but there is considerable ground water/ground seepage. During the digging process I left a 4 foot ledge which I have built up and sealed with a liner. My intention was to use this section, along with planting the edges, to filter the water. There will be no fish swimming, just me during the hot Florida summers.

I would like to begin building the bog filter but I want to do it right the first time. The filter is 3 feet wide by 15 feet long. The depth of the water in the bog is 14 inches. I plan on pumping water from the far end of the pool, and into the filter through a series of pipes with perforations which will be laid at the bottom. I think i have the general idea down but here is where I run into some issues.

The suggested rock for the filter is 3/4 inch pea gravel. This is mandatory to some but other people have found success using lava rock or other substitutes. My issue with this is there are no suppliers of pea gravel locally except for home improvement warehouses and I find their prices too high. Could i substitute a layer of bulkier rock at the bottom or a different similarly sized rock altogether (i.e. Tahitian Granite, River Rock)? I plan on putting river rock or granite in the pond bottom to prevent cloudiness and could get a discount by buying in bulk.

In addition, I am confused about the level of the water in the bog filter. Should there be some water over the gravel, lots of water, or no water at all?

 

[Mmathis]

@addy1

 

[budgenator]

I have a hard time believing that pea gravel is unavailable, I think some employee is saying you can't get it, when he/she really means we will not get it or tell you who can. Try talking to somebody at a ready-mix concrete company, my guess is they either have it for sale or know how does. The search term"construction aggregate" or "aggregate" may work better, Pea gravel specific product and is used in construction too much to be simply unavailble. With a 3 X 15 you're talking about 1 2/3 cubic yards or about 4500-5000 lbs.

Another thing I've noticed is there are a lot of hydroponics suppliers popping up all over and what the 420ers are using to grow their products isn't really much different from our bog filters, so they maybe a resource for growing mediums and substrates

 

[Meyer Jordan]

Need clarification on one point. Is this going to be a earthen-bottom or lined pond?

 

[Nepen]

I'm going to assume that you are going to line your pond with liner.

The problem with filling bog is the rock can be sharp and puncture the liner. You can use river rocks, that's what I used. the smallest size though. Or mix together. You can also use lava rock, just not at the bottom (sharp). Plants probably so better with smaller rocks for roots to hold.

I go tmine bulk from landscaping company that sell topsoil or mulch. You would have to have a truck or trailer or they have to deliver it to you. When I need a bit more i just buy it by the small bags from Home Depot.

 

[ASchell90]

Thank you so much this is exactly what i was looking for. I thought the same thing, if the product is everywhere someone has to have it, but the place i called specializes in landscaping rock which may be the reason they suggested something different.

Thank you again for clarifying it and pointing me in the right direction.

 

[ASchell90]

Need clarification on one point. Is this going to be a earthen-bottom or lined pond?

The bog filter is lined. I plan on the pond portion being earthen bottom. The entire bottom is solid clay for as far as i was able to dig.

 

[Meyer Jordan]

The bog filter is lined. I plan on the pond portion being earthen bottom. The entire bottom is solid clay for as far as i was able to dig.

I suspected as much. I would be very exacting in setting up the plumbing for this venture. The pump or pump intake must be raised to a sufficient height above the pond's bottom or you will quickly fill your "bog" with clay/soil. Adding gravel to the bottom of this pond is only a waste of money as it will eventually settle into the bottom and may prevent turbidity but for only a short period of time. You might want to re-think leaving this as an earthen-bottom pond.

 

[ASchell90]

Thank you. While searching i found this thread in which you posted an explanation - https://www.gardenpondforum.com/threads/new-bog-in-the-neighborhood.18375/

I am prone to making decisions while doing just enough research to support my wild notions so i appreciate your expertise and advice; i fear I may have gone too far with my plan without enough forethought.

It is my understanding now that the bog would quickly fill with sediment because of the amount of suspended solids in the water, correct? This would require cleaning out of the pipes and the gravel bed on a near constant basis due to the sheer amount of water being passed through the system. Lining the pond is an option but the intial investment is the main deterrent when compared to the piecemeal construction I am accustomed to. So I am at a point when i need to consider all options before proceeding.

If my ultimate goal is to increase water clarity and, for lack of a better word, health, what are my options if i proceed with an earthen bottom pond? Could I use the "bog" with the pipes on top of the gravel and still see some natural filtration from the plants? Maybe a fountain or waterfall into the gravel bed to increase aeration? I am unsure and just spitballing here.

I have already built the "bog" pond above the main pond, so i would like to utilize it rather than rip it out. I would also like to avoid the cost of purchasing a liner for the pond. Is there a way to naturally filter my giant hole full of water, is it even possible, feasible?

I sincerely appreciate your help with this. Thank you.

 

[ASchell90]

Would limestone gravel be ok or would that affect the ph balancd of the pond?

 

[Nepen]

I dont know other way. But I think since you do not want to have fish in, may be you can use some type of tarp / poster fabric (thin) just to line the pond. That will be cheaper and easier to still have bog to help with sediment. Bog is not very good at cleaning out sediment, though, especially the fine particle. The only thing that's good is something like quilt batting. in the bog, the gravel leave large enough holes for any fine things to pass through.

 

[Meyer Jordan]

Is there a way to naturally filter my giant hole full of water, is it even possible, feasible?

If your goal is water clarity, then you need to line the pond. Any mechanical filtration that would provide the desired clarity would be very labor intensive and really not practical. If you are looking to control water-borne pathogens a "bog" of the proposed size will provide absolutely no protection. If you want to utilize the already dug area for planting, fill it in with dirt and use surface flow.

 

[ASchell90]

Awesome, so the liner is key if i want clarity. I will look for inexpensive liner solutions that other have suggested in other threads. You're comment about my bog not being the right size to reduce pathogens piqued my interest. When i have installed the liner, will the bog still be useless in that regard because it is too small? I read that 10 to 15 % is adequate with no fish present. Do you have another recommendation for reducing pathogens that might be applicable to my situation?

It is really great to be able to pick your brain. Youre very knowledgable and helpful. Thank you again.

 

[Meyer Jordan]

A pond used for swimming will require the same disinfection as a commercially built swimming pool. This means, if you are really looking at protection, you have limited options. Your choices for adequate disinfection are Chlorine, commercial sized UV sterilizer, Ozone injection, and/or absolute 1 micron membrane filtration.
Wetlands (bogs) that are constructed to 'polish' filter Waste Water (sewage/storm run-off) do provide a certain level of pathogen reduction, but these sites are measured in acres and maintain a very low flow rate to allow natural predation. It has been shown that E. coli bacteria levels can be reduced to almost zero by certain zoo-plankton in a controlled environment in 48 hours. In a real life environment this predation rate may be quite different.
This leads back to your real options. All would require a certain level of maintenance and some are quite expensive.

 

[Meyer Jordan]

I read that 10 to 15 % is adequate with no fish present.

This applies only to Nitrogen/Phosphorus removal.