Gửi bạn hình FBF 1 bro làm cho bể koi:
TIGERCRAZE
Background
The pond was not purposely planned, there was a convenient space under the porch, ideal for a pond and waterfall but with no room for filtration. The pond is about 6 metres long, 2 metres wide at the widest point, and the depth slopes down to just less than 1 metre. The total volume is about 4000 litres, a small pond. Due to the position of the pond, the filter has to be higher that the pond and set away from the pond round the corner of the house. Also, because of the position of the waterfall, the return water must be under pressure, or it won’t come out.
Initially I used modified carbon filter with the medium replaced with graded gravel. Total volume of medium, about 200 litres. This matured slowly but provided excellent filtration. But the big drawback was that it got blocked up easily. In the end I was backwashing it twice per day and the return pressure was still low.
Possibilities
I had to make a customized filter that would not get blocked up, fit in the appropriate space and retain the pressure. I like the idea of shower filters, and have read good reports about them. Since then, Troy has also recommended shower filters. Unfortunately, shower filters only have gravitational return pressure from the height of the lowest tier.
I have read about fluidized bed filters, and already knew the principle. I liked the idea of massive bio filtration from a limited space. At the LFS area, there is a selection of imported FBFs, made of glass and Perspex, various sizes, looking very sophisticated. None of them were really big enough for a pond, they all looked too fragile, and, they were expensive for what they were.
The only real possibility was that I would design one and get one built.
Plan
In general, I tend to over design. So the plan I drew up was big.
I was also planning another pond, which I have since built and is currently curing. This is about 30,000 litres. I wanted the filter to be suitable so that I could use it, or a similar one, on this new pond.
I incorporated a few features into my plan that were not on the models at the LFSs.
- Tapered Cylinder: Most FBFs have a problem with tuning. It is quite easy both to choke them with too much sand, or conversely to have the sand blown out the top if the input pressure varies. With the tapered cylinder, fluidized sand always finds its own head, and within reasonable limits, it does not matter what size of pump or what weight and coarseness of sand.
- Expansion Chamber: At the top of the cylinder the expansion chamber slows the water down considerably to allow extremely light residue to settle.
- Asymmetric Blades: The water flow has a twist imparted as it enters the cylinder, to allow for extra aggravation.
Fabrication
The filter was eventually built in two machine shops. The main problem was that the tapered cylinder proved extremely difficult make. The machine shop that did the tapering and the lid specialize in non-uniform cylinders for export. They did a beautiful job.
The fitting was done at my brother-in-law’s machine shop,
Machine Inter Pack.
Installation
Starting Sunday morning, I striped out the plumbing on the old filter, removed the old filter, positioned the new filter, plumbed in the new filter. This took most of the day.
I use a 750 watt 3 phase submersible pump.
The medium was the finest grade of sand from the building supplier. I ended up using about 10 kilos. I had to stand on the rim of the filter, with the lid off, and throw in the sand one scoop at a time, so I could see down through the cylinder. The sand was so fine that there was a lot of dust that coloured the water yellow. This took about an hour to wash out by overflowing.
I then sealed the lid. The return water is through a pipe attached vertically though the lid. And I turned on the pump.
It did not work.
It didn’t work !
The pump was not strong enough, not even 750 watts. When the water was in the expansion chamber, it had overflowed without the lid on, but with the lid on and the return being in effect a vertical compression chamber, the water did not rise through the return.
I tried replumbing, but this did not help. It was by then Sunday evening. I called out the welder from the machine shop, but he could not come till Tuesday.
Two days for the pond to go without filtration. I did not feed the fish, but there was oxygenation. The moss on the waterfall began to dry out, and no doubt suffered.
Interestingly, after two days, I tested the water:
- PH: 8.5, a little higher than usual.
- Ammonia: zero
- Nitrite: between 0.2 and 0.5
- Nitrate: zero
I put this down to the surface of the pond, which is rough concrete, providing some minimal bio filtration.
On Tuesday, the welder, drilled a hole and fitted a downward return from near the top of the expansion chamber. I plumbed it again.
It worked.
Incredibly, the pressure at the waterfall is the same as if the pump were connected directly. The waterfall has never been so fast.
Maturing
For the 30 days after getting it working, I am replacing about 5 percent of the pond each day and feeding lightly. I will test the water once per week.
Really, I won’t know how effective the filter is for a couple of months. However I expect the filter is far more than my small pond needs.
I will update this thread periodically with results.
Costs
Oh dear!
It certainly cost much more than thought, even though I got it cheap, because my bother-in-law got the materials retail and built it at cost. I will ask him how much it would have cost for a commercial job, and I will post this later.
Another cost was in terms of time. From conception to completion it took more than a year. Most of this was in finding out how to get it done.
