My pool water become brownish color (refer pic) after some slack in pool maintenance, my bad


..... normally, I vacuum once a week, but this time round, I haven’t been vacuuming the pool for a month, but I still maintain the pool chemical and running the pump/filter.
When I decided to vacuum the pool, it seems like the filter is not doing its job. The brownish dirt on the pool floor seems like blown right back into the pool from the pool return. When I backwash the filter after vacuuming, I didn’t see any brownish water being wash out from the small sight glass.
I read that this might be caused by problem in the multi port valve, where the seal damaged, causing water to bypassing the filter material. However, after checking the multiport by hosing water into the various inlet/outlet, it seems like it working properly.
When I removed the multiport for checking, I also found that the filter material is well below the min indicator line, by about 1” (refer pic). I have been doing backwash and switch back to filter mode without doing rinse (not reading the manual fully) for the past 8mth, will this causes the filter material from being wash out, causing the reduced level of filter material? Would it be possible that the dirt particle is too small to be captured by the filter material?
Now, I am thinking of doing the following to troubleshoot:
- Run the filter for a longer period like 12hrs/d; normally I just run the filter for 4hrs. Vacuum to waste for all the dirt (seems like minute sand/silt) on the floor.
- Refill the sand to the recommended level. I suppose the filter will still works with the filter material lower than the recommended level, just that in a reduced efficiency?
Any recommendation?

