Reviewed by Andrada Simion, Master of Science in Chemistry
If your pool is blue but cloudy and you believe your chemicals are balanced, you should still double-check everything – perhaps by testing with different products and taking samples to different pool stores. A given test kit could be faulty/imprecise and a given pool store could give you wrong numbers.
If you’re absolutely sure everything’s A-OK, below are some non-chemical causes of cloudiness that should be looked into.
Environmental and structural sources
- Flora and fauna, whether it’s tree sap, pollen or animal droppings
- Wind and rain carrying dirt
- More people than your pool’s size can handle (especially for its filtration system), overloading it with things like urine, dead skin, sebum and sunblock. If the pool is accessible to outsiders, consider also the possibility of intentional mischief like pouring milk.
- Pool plaster and paint. Incorrect acid washing and cleanup can lead to plaster dust floating around. It can also happen after a new application which is nearly unavoidable, but even then it can be minimized by making sure that the plaster mix: doesn’t use soft water or too much water (and no water should touch it during and up to half a day after application), doesn’t contain calcium chloride and isn’t applied in freezing or torrid weather conditions. Brushing should also be avoided not only for newly applied plaster, but also for paint which even without brushing can create cloudy paint dust, more so for acrylic than epoxy paint and even more so if the paint job was done badly.
Valves, pumps and filters
There are many potential sources of problems in a pool’s filtration system that could mean particles that would otherwise have been removed end up clouding your pool.
- Valves. The wrong ones may have been left open or closed, particularly on settings meant to be used during maintenance like the ‘recirculation’ setting (exact naming can vary) common on multiport valves. Valves can also have the wrong attachments or have a damaged or ill-fitted gasket. Check also for cracks in the valve body.
- Pump function. If your pump has adjustable speeds make sure it’s not set too low, and remember that it needs to be left on for about 1/3 to 1/2 of the day (on the higher end if your pump is a bit small for the pool’s volume). If those things check out then things like lines filled with air (or blocked by debris) or clogged basket strainers can prevent it from doing its job. Pumps can also be damaged (or even catastrophically fail) from overheating which can be caused by reduced water flow efficiency (in turn caused by undersized pipe width or filter size, or angled plumbing close to the pump input), corrosion, poorly ventilated or high-temperature environment or bearing oil leaks.
- Pump impeller. The rotating blades that do the actual pumping experience a lot of stress and motion, and while they’re obviously designed to endure them it also means small problems can greatly reduce their function – from hard debris (like small rocks or stray pieces of metal) wearing them out (or simply due to age), to blockages caused by softer debris like lawn clippings or bits of plastic (check if it’s making a loud grinding sound), to threads that are broken or stripped (so that it’s no longer attached to the motor).
- Cloudiness could also be caused by air bubbles which can originate from air drawn in from various areas including skimmers (in case of low water levels), gasket/plug gaps, and cracked pipes/pumps.
- Poorly directed or an insufficient number of return jets can create poor in-pool circulation and prevent debris from even reaching your filters – they should be facing downwards.
- Blockages or crystallized deposits in filters, or reduced function overall. This is more likely if they haven’t been replaced for more than 2-3 years (meanwhile it should be cleaned every time the pressure gauge rises by double digits) or if too small a filter (particularly sand ones) is used with a too-powerful pump.
- Sand filter problems. Paths can form in sand filters (so that the water ends up skipping past all the sand unfiltered) if the sand becomes “sticky” (usually due to contamination) or if the pump is overpowered. Also using the wrong kind of sand (i.e. grains are too large) will reduce effectiveness, as will insufficient backwashing (often caused by doing it with a low setting on a variable speed pump), and sand loss.
- DE (diatomaceous earth) filter problems caused by things like DE loss (or accidentally forgetting to fill it in the first place – surprisingly common), broken bump handles and the internal structural mesh gunked up (with things like dead algae, grease and mineral precipitates – more likely if you neglect cleaning them or don’t do a thorough job of it).
- Cartridge filter problems such as the folded pleats losing their creases (caused by loss of the band surrounding it or by infrequent cleaning), damage during cleaning (by opening the filter rank without turning off the pump or through excessive sun exposure), wearing out from age or heavy usage (check for tears, holes or a ragged appearance) or not being inserted properly (especially if it consists of more than one part and you forget one of them).