Sand filters

The sand in a sand filter (#20 silica sand; 45 - 55 mm) is specially graded to trap particles in the 20 - 100 micron range. As a sand filter collects dirt, its efficiency increases, trapping more dirt. When your pressure gauge shows a reading 8 - 10 lbs. over its clean, start-up reading, it is time to backwash the captured dirt out of the filter.

"They Say" that a sand bed should be replaced after seven years. Gradual loss of efficiency may be hard to notice. If your filter requires frequent backwashing, every week or two, the sand bed may be "mudballed", or it may be "channeled". It may also "calcify" with calcium deposits. Other water balance problems may also contribute to sand deterioration, but a properly sized filter could go over 10 years between sand changes.

Use of Biguanide chemicals, i.e., Soft Swim or Baquacil require annual cleaning of the sand to prevent it from "gumming up". High amounts of bather oils can gum up a sand bed. And just the years of a pump forcing water over the grains wears away the sharp edges of the sand. Such sand becomes more circular, and traps dirt less efficiently.

Remember that for sparkling water, we need the trio of sanitation, filtration and circulation. If one of these areas is lacking, the water won't look so hot. So, if you've kept very good chemical maintenance and your circulation is good, you may have a filter problem. Is the filter sized properly? Many filters of the 70's - 80's were grossly undersized, the trend now in pool filtration is "Go Big Early".

Adding a small amount of aluminum sulfate or "alum", through the skimmer will form a gelatinous layer on top of the sand bed, useful in cleaning up an undesirable water condition. You can also add a small amount of DE powder or other filter media.

How do I Backwash my Sand Filter

When the pressure gauge is reading 8 - 10 lbs above the clean, starting pressure (after backwashing), it is time to backwash the filter. This process involves turning a valve so that the water will flow through the filter backwards, flushing out the dirt. Hence the name "back-washing." Sand filters can have either a push-pull valve (aka slide valve) or a multiport valve. The multiport valve has multiple ports on the valve, usually 6 positions:

• FILTER: Keep it here 99% of the time, except when backwashing, rinsing or wasting

• RINSE: Use this setting for 20 seconds after backwashing to rinse tank

• RECIRCULATE: Use this if the filter's broken; at least you're circulating.

• BACKWASH: Use this setting to reverse the flow in the filter and send water out of the waste line. Make sure valves are open or hoses rolled out.

• CLOSED: Put here to close off flow from the pool, usually to work on the equipment. Do not operate pump with valve in closed position

• WASTE/DRAIN: Another filter bypass setting, but this one sends the water out of the waste pipe (hose), instead of returning it to the pool. Used to lower pool water level or to vacuum to waste.

So, to backwash a sand filter with a multiport valve;

1. Shut off the pump motor.

2. Press down on valve handle, rotate valve from FILTER to BACKWASH position.

3. Roll out any backwash hose or open any waste line valves.

4. Open air bleeder assembly on filter, and turn pump on.

5. Watch pressure gauge for backpressure and hose for kinks. Be prepared to shut off pump quickly.

6. After hose fills with water, run for 2 - 3 minutes or until water runs clear.

7. Shut off pump motor and move multiport valve handle from BACKWASH to RINSE position.

8. Run on rinse for 15 - 25 seconds.

9. Shut off pump motor and move multiport valve handle from RINSE to FILTER position.

10. Turn pump back on and note lower pressure. Roll up backwash hose.

To Backwash a sand filter with a slide valve;

1. Shut off pump motor, roll out backwash hose (if you have it).

2. Twist to unlock plunger T-handle, pull/ twist plunger upwards 2 - 3".

3. Open air bleeder assembly on filter, and turn pump on.

4. Watch pressure gauge for backpressure (+ 40 psi) and hose for kinks. Be prepared to shut off pump quickly.

5. After hose fills with water, run for 2 - 3 minutes or until water runs clear.

6. Shut off pump motor and push T-handle back down into locked position.

7. Turn pump back on and note lower pressure. Roll up backwash hose.

A properly sized sand filter should, in most cases, be able to operate continuously for a period of 4 weeks between backwashings. A "Filter Run" of less than 4 weeks  may indicate sand problems (or sizing problems).

Sand in the pool?

Bad news. If it hasn't blown in, or been carried in on the feet of swimmers, it's likely coming from the filter. A broken lateral or standpipe may be the cause. You'll need to empty the tank, locate and make the repair, refill with fresh sand and test. After a sand change, it is not unusual to blow back small bits of sand.

Dirt is passing through the filter

This may be an indication of the need for a sand replacement. As pool filter sand ages, the sharp edges become rounded, and their ability to trap dirt decreases. This could also be an indication of channeling in the sand bed, or of a pump which is too large for the filter size.

However, even with new sand, and a properly sized pump, very fine debris passing through a filter, during vacuuming especially, is considered normal. If you are vacuuming and the dirt passing through the sand filter is more than you can stand - switch the multiport valve to the waste position, run out the backwash hose, and "vacuum to waste". The water will drop surprisingly fast, so you may want to add water before, during or after vacuuming to waste. Vacuuming to waste is a good idea if you are vacuuming out dead or living algae, mud slides, dust storms, mulch and other fine debris.

Sand bed replacement

To replace filter sand, you'll first need to empty out the existing sand. One method is to spread a tarp out beneath the filter drain assembly. Then remove the entire assembly, turn on the pump, and step back! The water pumping through the filter will remove most of the sand out of the drain hole. Another method is to remove the drain plug only and allow the filter to drain for several hours or days. Then, remove the top dome or multiport valve.

If you have the Triton style dome on the top of the filter, you'll need the octagonal dome wrench to remove the dome. Once the dome is removed, gently twist the baffle/pipe out of the way so you can get a scoop to the sand.......       (continued........)

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