What type of stone to use in bog filter

[GaryMoz]

Hi All, My pond construction is well underway.

I have an aquascape type deep bog filter with water storage under it, it's around 9m2 in area and 1.1m deep. So it will have around 700mm deep of stone.

I have a question on what type of rock / pebbles to use or not to use

I want 3 graduated sized of stone, Say:

100-200mm cobbles around 3 tonnes
40 - 80 mm pebbles around 3 tonnes
10 mm pea gravel around 3 tonnes

Here in the uk the larger cobbles and pebbles cost a lot £200+ per tonne. So what are the alternatives I can use or avoid, I can get 100mm -200m gabion filling limestone for around £60 -70 and cotswold stone too, . I want to avoid stone with sharp edges, so no flints etc.

An y suggestions?

 

[GaryMoz]

Does anyone have any insight on the stone to use, any do's or don'ts

Thanks

 

[Pablo]

I know a lot of people here go with the graduated size of rock in the bog. Start with the large stones and get progressively smaller to the pea gravel. Others go with all pea gravel, I did that, it is working fine but I have only had mine since last September. What I will warn you about is that the stone you get delivered is very dirty and trying to clean it is a chore before going in the bog. People will probably chime in with their tricks to clean it, some use screens. No matter how much you wash it off it will still be dirty and will make your pond water cloudy for several days, it does eventually settle down.

 

[GaryMoz]

The question was more about the type of stone, i.e coarse sandstone compared to granite., does it matter?

Large pebbles and cobbles are expensive so looking for alternatives unless someone knows where to get it cheap in the midlands, UK.

I'm expecting to have to clean it

 

[Pablo]

Well the Cotswolds is beautiful so the stone from there should be also I would think you want to keep with stones that are not too sharp to protect the liner. Not sure the actual type of stone matters as much

 

[GBBUDD]

The bogs success is that the rocks are rounded and graduated sizes. yes some have used nothing but peastone but They are also gold fish keepers.
The matrix bog will have 4" to 6" river rock for a single layer or two if that is what you prefer. there is no you must do this or that. then you cover that with 2" to 3" river rock for 4" to 6" that is then covered with 3/4 inch river rock.

River rock is a conglomerate of every type of hard rock that was beat up over centuries rounding the edges like a rock tumbler. They get lightly polished and this rounded edge along with the smooth rock allows the sediments to be pushed into the mass of rock, it gets trapped and is broken down by bacteria.. where it gets smaller and as it does it gets flushed out over time. So can it be a particular type and not a mix sure. Lime stone could be an issue as it can dissolve over time and if i am not mistaken it can raise the ph. To dangerous levels i do not know.

Can the rocks be flat with rounded edges or egg shaped or just a crazy shape again with rond edges yes they will all work. ANY ROCK WITH POINTED EDGES , OR THAT HAS FINES MEDIUM AND COURSE SIZE STONE IS WHAT WE DONT WANT AS IT WILL LOCK UP AND THE GAME IS OVER.

TRUST ME I GET IT THAT THE PRICE ADDS UP my bog cost me 6 k when i rebuilt it including liner, excavator rental, matrix and river rock . and that was for a 20 x 8 bog

Sorry for caps typing is not my favorite

 

[hitchins08]

I made my Bog a week ago using an IBC tank it already has a drain valve so I created a false bottom with filter grinding laid large rocks as 1st layer, and then 20mm pebbles halfway then completed with 10mm gravel so it finished just over the spillway. Just need to clad it and all will be good.