Can leaking filter valve cause filtration problems?

[Boeriemore]

Over the last few weeks I have on three occasions shock treated with three cup fulls of chlorine. I also
added a bottle of "booster" yet the water remains green/yellow.
A test strip confirmed that the chlorine levels, PH, total alkalinity and stabilizer levels are within prescribed limits. I also added 40 kg salt as the pool has a chlorinator. Filter sand replaced ten months ago.
I have a large lychee tree next to the pool and daily troops of monkeys create havoc, throwing lychees and
twigs into the pool resulting in the pool cleaner getting jammed by the fruit.
I am busy cutting down this tree and the pool is now free of this contamination, but still no blue water.
This morning when I switched the motor on cloudy brown/yellow water was pumped back into the pool,
probably what the cleaner had vacuumed up yesterday.
The multi-port valve has a slight cracked casing and after backwashing the extra pressure results in water seeping out from the casing. This stops after the pressure drops.
I was wondering whether air could be entering the system at night when the pump is switched off causing this problem. Any suggestions would be greatly appreciated.

[Larry]

If there's water coming out there can be air going in. I have found that air in a sand filter often causes the dirt to be blown back into the pool after the pump starts.
In overflow pools with the filter below ground, a leaky check valve will result in water passing the wrong way through the filter (on its way to the surge tank). When the pump starts you also get a cloud of dust blown into the pool.

Larry

[66616]

We had a leaky valve in July. After replacing it our pool became clear and we started using less chemicals and we needed less frequent vacuuming too.