Biological Filtration Design Advice

[ed2]

Hi guys,

With the start of the new year I've been giving some new attention and enthusiasm to my pond. Last year I lost quite a few fish and it turns out it was due to inadequate filtration (build up of ammonia) and lack of saturated oxygen.

I have since raised the sides of the pond, increasing the depth by 1 foot, which was a precaution for winter. The volume is now approximately 10,000 litres.

I want to really increase the stock of fish over this year and to avoid the annoying problems I had last year with unwanted algae growth, both causing at one phase pea-green coloured water and then, later in the summer, ridiculous amounts of blanket weed (which decided to show up 2 weeks after I bought myself a lovely little sterlet). At the moment, I'm unsure of the stock as I haven't seen the pond after winter. The water is quite coloured since winter and I've doubled my filtration.

The pond is now running with a 6,000 lph pump feeding a Hozelock Bioforce 12000 Pressurised filter with 13W UVC, and a 5,000 lph pump feeding a Blagdon 10000 Pressurised filter (it was a UVC filter but the weather got the better of it and split the casing and thus killed the electrics). This will be filtering the entire volume of the pond approximately once per hour. At the moment, the pond is set up with one filter supplying a waterfall, whilst the other goes discretely back into the pond under the bridge out of sight.

The pond is in front of a decking, with access via a bridge that goes over the pond. The wiring/waterproof switches for the pond are on the decking, as well as the two pressurised filters, which was tucked away in the corner. What I plan to do is to add a large biological filter in to the system, which I hope will help to further control the algae and boost water clarity and above all to manage the harmful chemicals.

I aim to install a gravel filter with planted watercress, as per this diagram: (Please excuse the low quality art!)

So the biological filter would be fed by both pressurised filters, which would act as pre-filters. The idea is that the water run through the gravel/stones and then overflow (gravity feed) back into the pond via the waterfall that is already in place. I also intend to plant the filter with water cress to try to use up some of the nitrates to avoid putting them back into the pond.

I plan to make a wooden frame and line it with soft ply wood boards, to make for a smooth and aesthetically pleasing container. I will then line this with a cheap liner material, such as tarpaulin or similar (I can't see a benefit of investing in expensive butyl or similar branded liners to just fill with gravel/rocks anyway?!). I will connect two pipes as shown to the filter, with a pipe sitting horizontally to spray the water in. This will then overflow through a wide bore pipe back over the waterfall and into the pond.

I also intend to put a mesh in approx 8 inches high, to suspend the gravel and allow waste to sink. I will put a large drain in too, for maintenance.

So, I would like some advice as I am still but a novice!

Is this an acceptable and positive way to filter?

Does my basic design seem ok?

Would it be better to put a long horizontal pipe the length of the box inside, with several down pipes to feed the water to the bottom?

Should I leave more than or less than 8 inches as a sump?

Any other general guidance would be appreciated too.



Thanks for reading and in advance for any advice,

Ed

 

[pecan]

I am pretty new to this and am just learning about filters. But I think investing in a good liner would be worth it. You don't want to have to re-do it because of a pesky leak. From you describe it sounds like it will work like a bog filter which I hear are very good. I am sure others on here will reply with some answers to your questions.

 

[fishin4cars]

I see a possible problem from the diagram, The planted area really should be pretty much unfiltered water. or at least only large debris should be removed before going to the planted area. The pressure filters should be on a circuit by themselves to help polish the water. The idea of plants filtering water should be looked at as feeding the plants. what your removing in the pressure filter is the food the plants need. I would run straight from the pond to the plant filter. keep the pressure filters and add a UV light that can be removed once the water is cleared after one of the pressure filters. This will help filter the water in more effective way and also do more fine polishing at the same time.

 

[ed2]

Ah yes! That is a really interesting point actually that I hadn't thought of! The main focus I had was more to bio filter with the stones with the plants to take the nitrates.

I have rethought slightly and had a play and I've tried setting up the two filters on the 6000 lph pump in line. So, I have the bigger filter first with coarse foams, a short 1 metre tubing section from that filter's output into the second filter's inlet, which has fine foams and some bio media (about half full with Flocor) and then back into the pond. So basically, I have doubled the size of the filter. I was worried it would put too much strain on the pump but it hasn't actually slowed the outflow at all as I can see.

This has made a pump available that I could use for the bio filter, feeding water directly from the pond. I have also changed the bio filter design slightly. The first third will provide 3ft x 2.5ft x 2ft (L x D x W) solids filtration. I intend to use brushes to do this. The remaining section will be 6ft x 2.5ft x 2ft (L x D x W) filled with very small stones. This should remove solids and still feed the planted section of stones

This is actually really exciting! I love doing DIY around the pond so I'm looking forwards to getting stuck in. I'll do some step by step photographs and put them on, it might be helpful for somebody else for inspiration!

 

[addy1]

For my bog/plant filter, I ran pvc piping down the length of the bog. Slots cut into the piping, the piping put under the pea gravel. The water is pushed up through the pea gravel/plants and waterfalls back into the pond.

Agree with fishin, you want dirty water to enter the bog, the plants will need it for the nutrients. You could draw the water from mid pond to keep the large debris out of the gravel.