Broken lateral, or is the dirt coming from somewhere else?

1Brush it, then feel it

Brush the debris and watch it, then rub some between your fingers.

No fizz doesn’t rule out scale: hard grey-white scale may be calcium silicate. Acid-test a small sample in a glass or ceramic dish, with eye protection and gloves, away from any chlorine product.

Where it collects is a clue. Filter media collects in a patch just below or in front of the returns. Dust and silt usually spread more widely.

2Stocking on the return

1. Vacuum the floor clean first, so you only catch what comes back.
2. Cable-tie a fine nylon stocking over the return nearest the filter.
3. Run in Filter and check the stocking after several hours.
4. Check again after the next pump start and after a backwash: lateral media often comes through in bursts then.

3Check the multiport valve

A worn or unseated spider gasket can let water slip past the filter bed, so vacuumed dirt comes straight back out the returns.

• Vacuum test: dirt puffs out of the returns as soon as you vacuum in Filter? Suspect the spider gasket first, then check the handle is fully seated and look for channelled or caked media or a broken lateral.
• Waste-line test: water out of the waste line in Filter usually means a worn or displaced spider gasket, or debris or a weak spring in the valve.
• Prevention: never turn the handle with the pump running. It’s a common cause of gasket damage.

Other clues

• Media in the pool straight after a backwash: most often the Rinse step was skipped or cut short, or the tank is over-filled. If Rinse was done properly and it keeps happening, suspect a lateral.
• Pressure stays unusually low and barely climbs between backwashes, with media in the pool: a broken lateral or channelled bed is possible. Rule out full baskets, low water and suction air leaks first. Record the clean-filter pressure after each media change as a baseline.
• Media loss shows up as a low bed level. Compare it with the fill line or the quantity on the filter label.

When it isn’t the filter

• Water out of balance. WA Health’s aquatic facilities Code of Practice recommends a saturation index between −0.5 and +0.5. High pH, high total alkalinity, high calcium hardness and warm water all push water towards scale. Test pH and alkalinity with a LaMotte Insta-Test strip or bring a sample in for a Spin Touch analysis, test calcium hardness with a calcium hardness reagent or tablet test, then check it with the LSI calculator.
• Very fine dust that keeps coming back. Sand only catches particles down to roughly 20–40 microns, so fine silt can pass even a healthy sand filter. Glass is marketed as finer, but silt can still get through. Use a clarifier such as AquaGUARD Crystal Quick so the filter can catch the clumped particles, or a floc such as AquaGUARD Crystal Express, then vacuum the settled floc to Waste, not through the filter. Follow the label.

Opening the filter

1. Dig the media out and inspect the laterals, hub and standpipe. Replace any that are cracked.
2. Replace sand more than about 5 years old, or caked or clumped. Glass lasts much longer: replace it only if contaminated, caked or low.
3. Fit new laterals whenever you change the media. They’re cheap compared with opening the filter twice.
4. Half-fill the tank with water before pouring media in, so the laterals aren’t broken on refill.
5. Backwash, then rinse, before setting the valve to Filter, to clear dust and fines from the new media.