Biological filtration stage
+ Draco Bio - a 185 litre box with two 110mm inputs at the top gravity fed from the drum filter output. This filter provides a massive surface area for good bacteria to grow and convert ammonia/nitrites into nitrates. In the filter will be 50 litres of Hex-13 bio media (plastic 'balls') that increases the surface area massively. The filter can take up to 100l of it, but for a 8000l pond this is fine.
The filter media circulates, stopping the water from going directly from input to output. It uses air to push the water up in the centre of the chamber. I'll use my existing 500l/h pump for that. .. water output is through two 110mm outlets at the bottom.
The Bio cycle is simply the nitrogen cycle:
Food -> fish -> Ammonia -> bacteria -> Nitrites (NO2) -> bacteria -> Nitrates (NO3) -> Plants or Algae (or water change).
Bio is one of the most important things as high ammonia or Nitrites (NO2) will quickly kill fish - as waste ammonia from Koi comes from both the gills and through pooping. The majority comes from the gills supposedly. However the bio will not work well without removing the poop before it decomposes or releases further ammonia/nitrites.
The bacteria in the bio section, the walls of the pond, everywhere will convert ammonia and Nitrites into the less harmful nitrates (NO3) which is what plants love.
Now comes the bit that makes the whole gravity feed work - the pump.
Pumping water out of the filter
It sounds odd thinking of it like this but the pump is simply emptying the filter, then the pond is pushing the water in to refill it. Like ezrider - I'll use a variable power pump, but the main thing with pumps is what it's pumping into - that reduces the flow rate. However the water by this stage should be clean so there's less wear and it doesn't get clogged up..
The pump I'll be using has 2" inlet and outlet with a maximum of 20,000l/h without any pipework or pumping the water upwards. They give the pump head height and flow rates for the pro range and by 3m vertically you're looking at 1/2 the flow rate (so 10,000l/h). I will be looking at using slightly bigger pipe - 68.8mm as you tend to get an easier flow rate through bends and once a bio film appears that larger flow rate will reduce slightly - it will still connect to the pump at 2" (approx 50mm) but all the piping will be this larger size.
A 63mm pipe gives a better max flow rate than a 2" pipe (I'd estimate a 63.8mm pipe is about 25,000l/h ideal rate with bends etc).
Next up sterilising the water - ultraviolet clarifiers (UVC)
UVs need time to sterilise the water (both tree water making suspended algae and parasites) that is flowing through them - think of watts of exposure per second. How much depends on how much sunlight, how many fish and how big the pond is (ie flow rate). Also the UV bulbs reduce in effectiveness as they age - so every year they should be replaced to maintain effectiveness.
Now comes the fun part - flow rate. A 110W UV has a 2" inlet and outlet.. However lower powers have only got a 1.25" inlet/outlet. Which is about 12000l/h absolute max in theory. This is far less as the lower diameter has worse flow characteristics and the EVO30 has two 90 degree bends in and two 90 degree bends out. However the EVO30 with 1.25" connections is quoted as 15,000l/h (yer right) for a 30,000l pond. Now I would be happy with 30W (I have a 24W on a ~4000l pond in full sun now) but the flow rate and restriction is concerning.
So one option is to parallel the UVC with a bypass that has a tap to vary the amount of water pushed through the UVC. Also another options is to make that 2 UVC in parallel thus creating a larger pipe area (although not completely double) this would increase the max rate capability without bypass closer to 16,000l/h but slow the water through (thus making the steriliser more effective) during normal flow rates. Any over rate needed can be taken by the bypass. It's better to have a dead bug at a slower rate. Option here could be to run two 15W UVCs or one 15W plus a 25W and then have one on a timer for over night.
There is another reason for considering smaller UVCs in parallel. a big wattage UVC typically has a larger/longer bulb and that means the UVC itself is long. A EVO30 is 98cm, whereas EVO15 and EVO25 are 58cm. This makes it easier to fit into a filter pit without having to have more bends to double back the pump flow. The idea being to maximise pipe area, flow rate and reduce the bends and height increase.
A US paper gives an example: "At an irradiance of 1.2 mW/cm2 calculated at the lamp aperture, 1 min UVC irradiation time reduced bacterial colony forming units (CFUs) by 99.1% on agar.", so a 30W is 30,000mW depends on the mW/cm2 over the area of the water (internal volume and time in the tube depending on flow rate). So a longer tube = longer radiance time of the water for the same flow rate, or double the length to double the flow rate (assuming wattage is over the required).
So given the bulb is shorter - this makes sense that the maximum flow rate to be effective is less.
Reducing the flow rate by splitting in two, then applying enough UV for that flow rate is valid.. just make more bulbs and connections but less horizontal space.
I see the output rising only a couple of feet above water level, so the pump will be pumping at its most efficient rate.
Feeding the plants.
Currently I have a small pool at the top of the waterfall - this is about 1 foot deep and holds a number of plants that have nitrogen fixing (ie removes nitrates) roots. I'd like to keep this idea as it works really well. It doesn't have to have all the water going through it, but I could split some directly over the water fall, then have a "stream" that is a long tough that holds lots of plants that then empties close to the water level.
I need to read up more in how I can do this in full sun for the new pond, given my existing veggie filter is in the shade. It won't bung up easily as the majority of the water will pass over the falls or with little soil (may use planting foam) the roots will be exposed anyway.
The output I'm thinking will be slow so it could be situated simply to pipe back into the pond.
I also want to have lilies in the pond, the issue here is that they should be on the opposite side of the waterfall but in sunlight - to essentially use the leaves as sun block to reduce algae on that side of the pond that receives the most sun.
Big Boyz Toyz!