Sand Filter Media - Tech Talk 43
There are numerous choices of media for sand filter vessels other than sand. For instance, you can use plastic beads, granular media of mixed size or lightweight filter media for particulate removal. Activated carbon can be useful for the removal of dissolved organics, chlorine, antibiotics, ozone, etc. Be sure care to replace carbon before it becomes saturated with the material it had previously adsorbed. Sand filters can also be used with zeolite, which is an ionic exchange mineral with the ability to adsorb ammonium ions from fresh water. Regardless of the media chosen, always backwash or rinse new material prior to operation to remove dust and fines that could irritate fish or cloud the water.
Sand filter housings can also hold biofilter media and perform as pressurized biofilters. This works well when using only one pump to cycle water from the culture tank through the filters to a height appropriate for spraying or degassing and then back. Filters can be put in series where two or more are used: one for particulates, one for dissolved organics, one for biofiltration, one for carbon, etc. Be aware that the published maximum clean water flow rate through a sand filter is typically much too high for aquaculture sizing. A flow rate less than half of the filter's maximum is what we recommend when selecting a vessel. In aquaculture, particular attention must be paid to backflushing frequency and volume. Recirculating aquaculture water's high organic content makes most media (especially sand) stick together and usually requires backwashing two or more times per day. Remember that sand filters are designed for sand media, which has a small grain size and heavy specific gravity. The use of any other media will require experimentation to find the best backflush water volume.