hi guys , i am interested in hearing your views on the pros/cons of fluidised sand filters - have had my DIY model for some time - if i get a zero reading in ammonia/nitrite can i assume that the biological filtration is working ok? it requires no maintenance whatsoever and i "top" up the sand every two months or so. it has a sand capacity of one kitchen bucket of sand (8l) and obviously runs 24/7 -unfortunately when eskom cuts so does the filter and i have to restart it again. any comments/suggestions?

Dear Koi158

I have a friend Clive Koetze in Retreat, Western Prov that uses a fluidised bed filter on his 13 000L or 18 000L koi pond..i can't remember the exact size. It works great and he claims that he can increease the fish load and feed of the koi in just one week. He claims that this filter "grows" the benefitial bacteria quicker than other type of filters...His Nitrification cycle seems to work very well as all the levels he test is 0 or close to zero.

On his setup there is one of the drawbacks that you get with his is that he can't put the full flow of his pump on the filter otherwise all the sand spills out.

You can also not use a Sand filter infront of the fluidised bed filter otherwise you do not have enough power to realy move the sand in the fluidised bed...so you must have your mechanical filters on the suction side of you pump and not on the other side....So no sand filters with a fluidised bed...which is not a bad thing in any case.

As far as i can remember this type of filter with sand as the media contains the biggest area for bacteria to grow on...even beating Kaldness....there are however debates on whether the bacteria on these fluidised bed filters ever get to a mature level because it gets constantly rubbed off by the other sand grains...remember Kaldness has a quiet zone where bacteria can mature in while sand grains do not. So when the power goes down your bacteria will not survive as long as on other medias because it hasnt had the ability to mature and to become more resistant. Mature bacterias live in what chris neaves calls slime cities. These slime layers actually protect the mature bacteria from the outside. Think of mature bacteria as Tartar on your teeth...yeah thats bacteria that has matured into a hard layer...now think how difficult it is to get rid of that.

So thats my 2c. Fluidised bed filters are great filter aslong as the pump does not go down.

thanks wayneb for your comments, yea you are right,it requires just the right amount of flow thru my fluidesed tower to achieve vigorous sand movement without throwing sand out of the top. i use a submersible pump to run all my filtration/uv/trickle etc so its easy to regulate the "tee" flow to the tower. just have to increase the flow to restart it whenever eskom shuts us down and then re regulate again as soon as its up and running again. admit i could have a major prob if we went down for 24 hrs or so though - have tested the thru flow of the tower and know that it works all the way down because when i empty the sand out of it , the sand is clean right down to the bottom of the tower - oh and providing my non return valve is working, the pump restarts the filter without any help from me if the shutdown is not more that an hour or so. i think i am overstocked though! have a total of 16 fish - 1x50cm 4x40cm 3x30cm and 8x20cm - my vol is only 8000l so my gut feel is too many fish but my ammonia/nitrite/nitrate seem to remain at zero - my total alk hangs around 5.0 and my ph 7.9 - what do you think? cheers dave

Where getting a bit sidetracked from fluidised sand filters...

If my calculations are correct then you are under the required 66cm/1000L requirement. You have 460 cm of fish and a 8000L koi pond. So 460/ 66cm = 6.969 * 1000L = 6969L required for your koi. a 8000L koi pond can support 528cm of fish. Dealers usually say 1 fish for every 1000L but they are talking about big kois....but keep in mind that your koi will grow.

The stocking level issue can usually be controlled better by throwing better and more filters at the pond but the reason stocking levels are calculated a 66cm per 1000L is because of the oxygen requirements of the fish.

66cm per 1000L gives you roughly 2-3hrs of oxygen if saturated to the max. Smaller fish can obviously live longer on the same amount.

Remember never mind how many Airpumps and water falls you add, water can only contain so much oxygen in the end.

If the power does not go down ever you can have a 10 000L pond with a 100 fish in it providing you have a good return with decent filtration.

Never heard about it can someone please send a pic

Heres some images that i found on the net.