The first option is a malfunctioning filter. That is why I recommend you to backwash the sand filter and then filter the water over a long period.
A properly functioning filter is very important for clear and healthy pool water. Choosing a high quality sand filter, for example from Pentair, is important. Because cartridge filters do not filter the water as well.
When using chlorine tablets or granules, the unclear water can be due to a high concentration of cyanuric acid. This effects the functioning of free chlorine which could cause green swimming pool water.
Therefore measure the concentration of cyanuric acid, which may not exceed 70 mg/L. An excessive level of cyanuric acid can be decreased by adding water to the pool. But it can also be avoided by using liquid chlorine.
A too high concentration of hardness is another possible cause of cloudy water. This cloudy water is caused by the lime in the water. Measure the calcium hardness of the swimming pool and reduce the calcium if necessary.
A good concentration of calcium is between 100 and 200 mg/L CaCo3. The ‘Anti Calc’ product of Melpool can help you fight a too high concentration of calcium.
The last possibility brings us back to your sand filter. Cloudy water can also be due to small particles which are not absorbed by your pool filter.
Use the HTH flocculation-chemicals ‘FlocFix’ to remove those particles. The pH should be between 7.6 and 7.8 for a proper functioning of the flocculation-chemicals.
