On uplow gravel filter, how are rocks supported?

[tryeager]

I'm about to construct a 24" deep upflow gravel filter, and I'd like a small chamber under the rocks to equalize the flow across the area and serve as a small settling chamber for occasional backflushes. I've seen lots of drawing and descriptions of this idea, but nowhere have I found what people use for the grid that must support the rocks. For my barrel filter I used an old style flourescent light fixture grid to support onion sacks, but that's not strong enough for 2' of gravel over it. Is there an inexpensive plastic grid that people use?

 

[addy1]

bread racks, if you can find them work great.

 

[ididntdoit99]

Couple idfferent examples from the DIY section, using a milk crate or tubing to create a support.


http://www.gardenpon...doc-bio-filter/ first post has pictures

http://www.gardenpon...r-skippy-style/ post number 8 has pictures

http://www.gardenpon...ck-tank-filter/ post 2 has pictures.

 

[sissy]

I found a bunch of old trays at the dump from a nursing home and they worked great just drill holes in them.I guess they from thee cafeteria.

 

[addy1]

I have used old dishwasher rack to support things they are tough. Check a store that sells appliances, they may have some dishwashers they would let you take the racks from.

 

[sissy]

Or go to your local recycling center and watch for a guy coming in with a dish washer or you can ask the guy who runs the metal recycle center they sort most of that stuff out on the side .

 

[Catfishnut]

Tryeager,

I was assembling a sediment filtration tank using a 55 gallon HDPE barrel. I was having a tough time finding anything that fit the circular shape and size of the tank. Let alone something that was sturdy enough to support 3-4 inches of broken marble, 3-4 inches of river pebbles and 4-6 inches of river gravel.

I finally made my own. I found a scrap piece of 1/2 polyethylene sheeting. Cut it in a circle form and spent quite a bit of time marking and drilling 7/16" holes all over it.

To support this off the bottom, I just used some short pieces of 2" PVC tubing for legs underneath this platform. You can construct an actual framework out of PVC piping and fittings that would be more stable (won't fall over).

If you can find the materials and have the time, it can be very inexpensive and you can make it any shape you need.

The pix below show the platform and then inside the tank. Cannot see the supports underneath, though. The PVC at the bottom of the tank is drilled full of tiny holes. I will use this for purging the sediment filter (rock) with compressed air and water when cleaning is required.

Gordy

 

[fishin4cars]

Can I ask, Why do you want to use rocks for the upflow filter? Is there going to be plants planted in it? If not there are amny kinds of other filter media that are far less weight, easier to work with and have much much more surface area for the bacteria to grow on. Most can be slightly more expensive but the benefits will out weight the gravel many times over and the cost difference should be that great.

 

[Catfishnut]

Can I ask, Why do you want to use rocks for the upflow filter? Is there going to be plants planted in it? If not there are amny kinds of other filter media that are far less weight, easier to work with and have much much more surface area for the bacteria to grow on. Most can be slightly more expensive but the benefits will out weight the gravel many times over and the cost difference should be that great.

Fishin4cars,

I don't know if you are asking me or Tryeager. But, for me it is going to serve as a sediment trap filter (not a bio-converter). I plan to screen the pond (bait tank water) for heavy and bulky solids in the sediment filter before it reaches the bio-converter tank where I will be using Kaldnes K3 media as a rolling bed type filter.

If you have a recommendation for an alternate to the rock and gravel bed, I would be open to suggestions. I simply modeled that design after watching artesian springs out in the sandhills of Nebraska. Where the water percolated up through gravel and sand and came up to the surface crystal clear and ran into the river.

Gordy

 

[fishin4cars]

Gordy, in your set-up with the Kaldnes K3 media I can understand better why you would want to use the gravel bed. as for using it as a primary Bio filter it just seems to me a lot of extra weight and no benefit for just a bio-filter media. In a bog filter yes as it serves multiple purposes. In a standing free flowing filter I can't think of any great benefit of using gravel.

 

[Catfishnut]

Gordy, in your set-up with the Kaldnes K3 media I can understand better why you would want to use the gravel bed. as for using it as a primary Bio filter it just seems to me a lot of extra weight and no benefit for just a bio-filter media. In a bog filter yes as it serves multiple purposes. In a standing free flowing filter I can't think of any great benefit of using gravel.

Yes Fishin, I wouldn't rely upon the rock and gravel bed for a bio-converter system either. It would have too many disadvantages, or too little of an adantage primarily in regards to surface area. It would be a very rough and crude floating bead filter system. It would not provide sufficient bio-conversion because the surface area is lacking in the first place. Secondly, it will eventually clog with pond debris and so it requires more frequent and vigorous purging or backwashing to cleanse it. If I relied upon this for the bio-converter area, I would lose a lot of the viable bacteria culture during the cleaning and purging process.

So, I want this portion of the filter system to simply provide a back pressure on the system to slow the flow just enough to drop out most of the sediments in the bottom of the sediment tank and capture the remainder of smaller and lighter wastes amongst the rocks. That dirt and debris will be captured in that sediment filter tank (this is what I am calling a prefilter for my bio-converter) so that the bio-converter just gets the ammonia laden water to work on, and none of the mechanical debris.

Basically, I am trying to create a multi-stage filtration system. It is still a work in progress, and I am adjusting items as I go through learning and research and my own trial and error approach.

Gordy

 

[tryeager]

Thanks for the suggestions, Forum. I'll look for some bread racks, nursing home trays, dishwashers, milk crates, polyethelene, etc, and probably end up with a combination of some of those, since I need about 15 square feet for my 3' radius semicircle bog filter planting area which hopefully will totally replace my barrel filter.

tryeager

 

[Waterbug]

15 sf, 2' deep is about 1.43 tons of pea gravel, if that's the gravel.

I just use some large rocks, broken bricks, whatever, around the drain, some smaller rocks over those. Doesn't have to cover the entire bottom, just keep the gravel from being flushed. In a flush gravity isn't the primary mover, water movement is. So stuff flushes just as well horizontally as vertically if that makes sense.

I would be careful of anything with small regular holes. I think the pea gravel jams and plugs those. Been there.

 

[addy1]

15 sf, 2' deep is about 1.43 tons of pea gravel, if that's the gravel.

I just use some large rocks, broken bricks, whatever, around the drain, some smaller rocks over those. Doesn't have to cover the entire bottom, just keep the gravel from being flushed. In a flush gravity isn't the primary mover, water movement is. So stuff flushes just as well horizontally as vertically if that makes sense.

I would be careful of anything with small regular holes. I think the pea gravel jams and plugs those. Been there.

i faced all my slots down and out sideways 45 degrees or so, none pointing up. That way the peagravel can't drop into them and jam the openings.

 

[Catfishnut]

i faced all my slots down and out sideways 45 degrees or so, none pointing up. That way the peagravel can't drop into them and jam the openings.

Addy,

I will layer my rock bed in my sediment filter so that each layer is progressively finer as you go upwards.

The broken marble rock is too big to fall through the 7/16" holes in my platform grating at the bottom. The smaller river rock or pebbles will lay atop the marble and cannot fall through it, nor can it go through the 7/16" holes either. The pea gravel won't be able to get down through the river rock/pebble layer and on and on as it progresses upwards.

When I need to purge the sediment filter to clean it at whatever interval I find is necessary, the boiling action of the moving water and high pressure air coupled with the size and weight of the different substrates will naturally expand the filter bed to some extent, but it won't intermix them except to a very small degree simply because of the physics of bouyancy. The finer particles will always organize themselves to the highest layers.

I was going to use some extremely coarse sand (about 1/8-1/4 dia of pea gravel) as the final, top layer, but judging from Waterbug's experience with a sand filter plugging so quickly, I am going to leave that layer out. I am thinking that pea gravel is as fine as I will need (or want) for the sediment trapping that I need and desire, without plugging up too quickly.

For cleaning this sediment filter, I can apply three functions, in stages. Gravity flow, water flow and vigorous aeration.

My envisioned steps for cleaning this sediment filter:

1] Open the 2", bottom drain line and let the water flow extremely rapidly via gravity and suck all the heavy debris out from the bottom of the tank and the lower portion of the rock filter layer (mainly the marble). Close the drain.

2] Use the incoming water flow from the tank (pond) and the high pressure aeration from my PVC array at the bottom of the filter barrel to aggresively boil the water and rock media upwards. With the outlet to the bio-converter barrel closed off and the overflow line open, I would let the dirty purge water outflow into the lawn until it appeared to clean up well.

3] Repeat steps 1 and 2 until the visual clarity of the water in both steps reveals that the process is completed satifactorily. Then, I just turn the system back on to route the water through the sediment trap/filter as usual.

I do know that this will work, I just don't know if it is going to work to my satisfaction. I may have to make some adjustments to fine tune it. The key for me is the size of the rocks and their density and the high pressure/high volume air for purging. I must have a very aggressive boiling action in the top (finer media) layers for it to function well. It must clean the heck out of the smaller media and reorganize it so that the "pores" through the media for water flow remain open, but not channelized. I expect some bacteria to be living here on this media. Some of the live, beneficial bacteria cultures that get washed out of this media will find their way into the bio-converter barrel. Most will become lawn fertilizer, unfortunately.

The cleaning schedule will have to be determined and it may vary greatly, depending upon my bio-load, weather, and many other factors. My system is not going to be anything like a typical garden pond or fish pond as I will be moving dirty fish and dirty water in and taking clean fish and clean water out on a continual basis. This is, after all, a glorified bait tank. I think you can see that this is a dilemna that I must engineer a design to accomodate or compensate for or else I must simply just put up with some additional maintenance to contend with it.

I may not end up with the most perfect "pond" in this endeavor, but I will certainly have the best doggone bait tank!

Gordy