hi people. i am a new member on this forum so please be patient with my queries. i am totally confused re the "best' method of mechanical filtration - some koi experts swear by swimming pool sand filters and some abhor them and say they are the very very worst for koi ponds! so just where does the real truth lie?? my pond is 8000l has reasonably clear water - have 16 fish all sizes from 50cm to 20cm - do i add a sand filter or not? dave

Hi there

Before the numerous power outages, my view was as follows:

The typical way to filter your pond mechanically is to use a sand filter. Quite a lot of pond keepers will tell you that a sand filter is an absolute no no and should only be used in swimming pools combined with chemicals. We believe that this attitude derives from many web sites written by dealers who are trying to sell their high tech bio filters and therefore break down the use of sand filters.

Disadvantages:

If filter sand is used, you will definitely have numerous problems with clogging of the filter. Use bigger gravel to solve the problem.

If you bypass your filter for longer than a day (due to lack of oxygen) or do not backwash regularly, you might have problems with nasty bacteria. It is crucial to backwash your filter if it was not running for a few hours.

There is a fairly big initial capital outlay because you need a stronger pump ( R 1100.00) (to backwash the filter effectively and push the water through the gravel bed) and your filter will cost you approximately R 1000.00 and your gravel will cost you approximately R 300.00 ( R 100 per bag) A submersible pump will not work.


Advantages:

It is an extremely convenient way to keep your pond crystal clear by a simple backwash once a week. You can do this even on your way to work with your suit on and takes only a few minutes. At the end of the day, you want to enjoy your pond and do not want to clean huge dirty filters by hand, which is sometimes a mission.

The average sand filter provides approximately 150 square metres of surface area for bacterial growth which in itself is a form of a bio filter and is normally sufficient for a 10 000 l pond. Combined with a small bio filter filled with for example alfagrog or lava rock, you will have sufficient mechanical filtration and enough bio filtration for even a 20 000 litre pond provided that your stock level is not too high.

It can be combined with a settlement chamber where all the major dirt settles in the chamber to be flushed out from time to time, before it even reaches the sand filter, leaving maintenance to the sand filter to the minimum.

Damage to the biomass(beneficial bacteria to be maintained) is minimal with backwash.

It looks neat and can be buried or placed far away from the pond.

Compared to the latest bio filters, the capital layout is not that big and it is very durable, lasting for many years.

It is easy to bypass in case you have to medicate, using the simple valve. Before you resume, do a proper backwash to avoid problems with nasties.

Although it clogs up from time to time, it can be opened easily to enable you to stir any crust developed at the surface before you backwash. For this purpose, the Koi filters have a lever to easily open and close it, as opposed to the swimming pool filters that have to be unscrewed.

It comes with a valve to easily channel the waste to your drain by using the waste feature, especially if you attach a vacuum to the inlet.




However, due to all the power outages, I recommend that you rather stay away from a sand filter. If the power goes down for two hours, the beneficial bacteria in the filter dies of and the nasty bacteria goes crazy due to the lack of oxygen. When the power goes on again, all the junk goes directly into your pond unless you bacwash after each power outage. (Which is often difficult)

Also remember that there is a difference between a swimming pool sand filter and a Koi sand filter. You should never use a swimming pool sand filter, because the holes of the arms inside is too small and can not be opened easily to break the crust. You should also never use sand, only gravel or other modern products(plastic) that came on the market recently.

thanks for your informative reply paul, but help me out here please, if the uv lights kill off the stuff that makes the water go green, and the sand filter sand prticles are too large to trap the sludge formed by the "dead' from the uv lights how do i keep my water clean? paul just bear with me please, i understand that mechanical filtration means a physical method of straining the visble floating junk out of the water. the sand filter is not able to do this because the sand is too coarse ? so am i left with only settlement chambers to collect this "fine' junk? and what stops it accumulating in the sand filter anyway? my pond is in full sunlight and the uv's work overtime to create sludge which settles everywhere including in my filters. i have a simple settlement chamber plus a large trickle filter - if the sludge is allowed to form a thick (50mm) layer in the settlement area are my fish at risk? appreciate your comments cheers dave

The amount of "sludge" created by your UV light is minimal. The sludge that your should worry about mainly comes from fish waste, decomposing leaves and left over food(but also the killed free floating algae). Most of the debris should be trapped in your settlement chamber and your settlement shamber should be emptied on a regular basis. Sludge of 50 mm can an will eventually create problems. The nasty bacteria loves the sludge.

Surely your settlement chamber has a waste valve which can easily be emptied on a regular basis? This is the whole idea of a settlement chamber. A way to get rid of the main debris easily. Without a waste valve, it is senseless. The flow through your settlement chamber should also be limited, otherwise too many debris will go past this filtration stage. The sand filter would only 'polish" your water before re-entering your pond.

If you use sand, it will clog up every few days and limit your water flow dramatically or even stop the water flow. The gravel is quite effective, even to filter the tiny debris.

Hi Paul, yea its makes sense, but of course we all wish we knew the best way to design the pool before we actually did it ! now im faced with what i have and must manage accordingly. trying to "stretch" my siphoning of the sludge from my settlement chambers to as long as reasonable without harming the fish - they work so darn well that they build up sludge very efficiently, hence my question re the 50mm depth before siphoning - guess this would take about one month so im gonna try for the first of every month. have a very good DIY fluidised sand filter column to take care of the biological filtration as well as a very large trickle filter. my waterfall aids water oxygenation - my total alk is kept at just above five and my ph around 7.9 - salt content very low (1.002) where my marine tank is constant at 1.024 using the same swing lever meter - have only water lily type plants, separate from my koi, and have night lights over the water to attract insects for late night snacking - pond turnover thru filters is around at 7000l per hour - so why dont my fish spawn?

The best advice I can give you in the circumstances is to get one of those manual handheld vacuums to clean your settlement chamber on a regular basis, unless the siphoning works for you. Some people use the two methods in conjunction with each other.

All the other aspects sounds fine in your pond. I assume that you made a typo with the 50cm fish. If not, you are totally overstock. Maybe you should try to induce the spawning in September/October. See our website and spawning topic on the forum.