Pond Design & Filtration

Hi everyone.

After a bit of advice. I am going to be starting a raised formal pond, dimensions are 4m diamter and about 2m deep so a quick calculation gives me about 25000 litres. I will need to filter this so I am after some advice on general filtration etc.

The pond will have some fish, of which sort I am not too sure yet.

I know the question is somewhat vague, but I amn quite new to this pond stuff.

Rob

 

Well please remember to check your structural calculations first Robert! That's 25 tonnes of water pushing downwards and outwards in a raised structure.

As I understand it there are three main kinds of filtration types: Physical (like in a swimming pool) that takes out the solids, 'Biological' which passes the water over a porous aggregate that has been colonised by bacteria etc whose main purpose is to oxidize the nitrites released in the fish waste into nitrates which are less harmful to them, and plant based filters like reed beds which actually remove the nitrates and other potentially toxic compounds.

In an ideal world you would put your water through a biological, then a plant based, then a physical filter. Best to start saving now...

Alternatively the most common used is the biological filter,. In this case I reckon it is essential to use at least two seperate filters and to regularly clean each of them (not at the same time)to prevent build up. Note that you MUST remove some of the water from your pond every so often (usually as filter backflushing) to prevent build-up of nutrients and toxins, as the biological filter does not actually extract any nitrates or phosphates from the water, and they build up causing many problems - the most common of which is filamentous algae which clog the pond pumps and look unsightly. Try to have marginal/aquatic plants if you can to provide shade, strip the nitrates out, and to increase the diversity of the aquatic life.

Hope this helps

 

Jazid

Thanks for the reply regarding the filtration.

Only a small portion of the pond will be above ground, approximately 450mm so the weight has been considered in the construction of the pond.

Best regards

Rob

 

Hi Robert I would advise you install a decent filtration system and which sort and what size will be determined by what you keep in the pond from the depth of it I would assume you may be thinking of koi remember to the running cost of the system biological filters need to run 24hrs a day 7 days a week,a quick summation you would need a Aquashift st4000 Dirty Water Pump(only takes 85watts)coupled to a Hozelock ecomax 9000 combi filter with built in u.v.sterilizer this combines the biological aspect and will filter out solids the u.v. light clumps together algae cells and they then get filtered out you still need to do partial water changes as Jazid says and you need to be careful how many fish you put in over stocking is easy to do especially with koi each fish when well fed can grow up to 30" they don't limit their size to the container they are in unlike most fish

 

I would be thinking of a multichamber filter fed by 2 4" bottom drains. Whoever is building the pond could also build the filter which would be much cheaper than buying one from a dealer but needs some DIY skills. The UV before or after filtration is an ongoing debate but I tend to go with after filtration which has always worked well and is easier installed at the outlet stage. You really need to decide what you intend to stock with as this will dictate the filter size but you can never build it too big and it is always better than realising too late that you should have gone bigger. If Koi then consider a vortex to remove the solids then the multichamber for biological filtration.

John.

 

That`s a fair sized pond.
If the pond is for koi you will need to consider moving all that water (25000L) through the filter as a rule of thumb, ideally once every 2 hours.

You have about 880 cubic feet of water which needs filtering..so the filter will have to be pretty huge too.

Even if it only about 5% of the pond volume (1275L), you`re looking at 45 cubic feet (6` x 3` x 2.5`)
This will allow about 6 minutes in the filter at the rated flow for the bacteria to do their work.

 

Thanks for all the replies, however I have had to reconsider the size of the pond as I have found a fresh water well smack bang in the middle of the pond and the water level of the well is 1 meter below ground level.

So, the pond will now be 3.4m diameter by 1.5m deep so as its in direct sunlight, a volume of about 16000 litres.

In terms of stocking the pond, I am not going for a pure Koi pond, it will be a mixed pond with maybe 2 or 3 koi and a mixture of other fish.

There will be planting at the back of the pond with a waterfall in the back center of the pond.

Is there a specific requirement for a bottom drain? Could I not use a bottom pump in the pond connected to a pressurised filter system such as a Fish Mate 30000, suitable for a pond with 30,000 litres?

Thanks

Rob

 

Hi Robert
Bottom drains are ideal if you can install them as the pond bottom is sloped towards them.

You could design a slope into the base and use a pump in the lowest part, but it won`t be anywhere near as effective as the 4" diameter outlet of a drain.

A reasonable sized multichamber filter would be better than a compact pressurised one..if you have the space for it.

 

The main benifits of the bottom drain are ease of maintainence and that the filter is gravity fed and you pump back to the pond. Fitting a bottom drain is slightly more expense but you save on the price of pump. The flow rate for your pump is with no restrictions (no tubing attached)and zero head which is the height the pump has to force the water from the bottom of the pond to the filter. Once you attach tubing to pump water through and you are also pumping uphill the flow rate is greatly reduced and you will need a much stronger pump than originaly thought. With the bottom drain system the filter is gravity fed and you only pump from the filter up a much smaller height and through much shorter tubing either back to the pond or to the top of a water fall. Therefore flow rate is maximised and generally a smaller pump will suffice. The pump in the pond system also has the disadvantage of the pump frequently blocking and needing removal for cleaning etc. If placed at the end of the filter system it pumps clean water back to the pond and much less maintainence.

John.