The Bad News about Sand Filters in a Fish Pond...

The question of sand filters in a fish pond comes up regularly. Jeff's problem is a very common one. If you have a sand filter this is a MUST read

Hi Tony,

Thanks for putting together such insightful information about Koi, ponds and everything in between. I have a problem and I can't seem to find the right solution.

I have had a pond for roughly 2.5 years. It is approx 4000 gallons, has a waterfall with two sections, and also a pipe at the bottom of the pond to move the water on the bottom. There are two bottom drains that connect and go to a .25 hp Artesian Pump. This then travels thru a UV light 25 watts to a Hayward Sand Filter (vari-flo valve rated, pressure 50 PSI/3.4 BAR, rated flow 28.5 m3 /h with 300 lbs of 12 gauge silicon sand). The water then travels back to the waterfall and (bottom pipe) but first goes thru another 50 Gallon filter with layers of Japanese Matting for a final cleansing. The distance from the pump/filter to the waterfall is about 40 feet. 90% of the piping is flexible and there are only 2 90 degree angle joints. I have approximately 35 fish (half approx 12-14 inches the rest smaller down to approx 4 inches; I know, too many fish) Ok, got the basic picture?

Here's my problem which started happening at the beginning of this year. For some reason the pressure returning to the pond gets less and less, down to almost zero a few days after I do a back wash. For the first two years this did not ever happen once. The pressure would eventually go down after a backwash but it would be after a few weeks, and never down to practically nothing. Here is what I have tried:

· clean Hayward filter (2 times)
· clean 50 gallon Japanese matting filter (1 time)
· change out pump (first pump was a Hayward NorthStar 1 hp) Although the Artesian is only .25 hp the pressure seems fine right after a backwash or when I put the filter to re-circulate (then it is very strong)
· change out as many joints as possible and replace as much piping as possible to flexible piping
· cut off the bottom two drains and put in a drain that hangs over the side of the pond and then connects to the Artesian pump (maybe something got trapped in the bottom section of the two drains?)
· disconnected the return piping to the waterfall and bottom pipe so that it only goes through the 50 Gallon filter and one part of the waterfall.

At this point the only thing I really haven't changed out yet is the filter. A person who owns an aquarium said I should get rid of the sand filter (out dated) and put in a plastic bead medium bio-filter. He said the problem is the sand gets too compacted which makes the backwashes ineffective, plus it puts more pressure on the pump. This makes sense however it was not a problem for the first two years of having the pond, plus I cleaned the filter thoroughly twice.

Do you have any ideas as to why I lose all the water pressure after a backwash in only a few days? Thanks!

Jeff ,

Los Angeles, California

Response... Sand Filters in Fish Ponds are Bad news

Jeff... sand filters are BAD news on a pond. They are great for pool where chlorine is used to kill bacteria and algae

The sand gets blocked by algae (very tiny particles which clog flow paths) and it becomes virtually impossible to run the filter for any length of time. Alternatively the bed of sand becomes compacted in some areas while not in others reducing area for flow and chances of anaerobic bacteria build up and ultimately fish disease problems

Solution...

If you want to keep the sand filter then change from sand to a course pond filter medium such as Supra (Alfagrog in UK and Alfagrog South Africa) which also acts as a very good biofilter medium. This is probably a good choice since you already have all the equipment installed. You don't need to fill the sand filter... use enough to create a bed of say 12 inches deep. This will be enough to catch most of solid particle. You will still need to backwash regularly even though pressure gauge might suggest you don't need to.

Alternatively dump the sand filter and use a basic biofilter also use Supra in this filter... this also gives you opportunity to save on power consumption but you will have to buy a new pump

Regards

Tony