Bizarre dirt problem in pool

[waterbear]

Can you describe the dirt (color, etc.) and where in the pool it is located? Also could you post a set of test results so we can possibly rule out some causes. Remember that there is a lot more turblance in a hot tub so any dirt would remain suspended in the water while in the pool it would tend to settle to the bottom, as Watermom pointed out.
Could you also let us know how you are chlorinating (SWCG, trichlor feeder or floater, liquid chlorine or bleach, etc.) and the type of filter (sand, cart, DE--not sure what you mean by 'filter bags; but suspect you either have a DE filter (the term is 'grids' or 'fingers' depending on design) or a cartridge filter. Also, does your pool have an automation system to switch from pool to spa automatically (and if so what kind) or do you have to manually switch valves?

[JimK]

... Remember that there is a lot more turblance in a hot tub so any dirt would remain suspended in the water while in the pool it would tend to settle to the bottom, as Watermom pointed out.
........

I was thinking the same thing.

[MattW]

Can you describe the dirt (color, etc.) and where in the pool it is located? Also could you post a set of test results so we can possibly rule out some causes. Remember that there is a lot more turblance in a hot tub so any dirt would remain suspended in the water while in the pool it would tend to settle to the bottom, as Watermom pointed out.
Could you also let us know how you are chlorinating (SWCG, trichlor feeder or floater, liquid chlorine or bleach, etc.) and the type of filter (sand, cart, DE--not sure what you mean by 'filter bags; but suspect you either have a DE filter (the term is 'grids' or 'fingers' depending on design) or a cartridge filter. Also, does your pool have an automation system to switch from pool to spa automatically (and if so what kind) or do you have to manually switch valves?

That's a very interesting point about the water turbulence in the hot tub; I hadn't thought of that.

In answer to your questions:

1) The color is light-ish brown, a typical dirt color (sorry I can't be more specific - I'll try and take a picture next time) and it seems that it's quite fine matter (it's not clumped up as lumps of mud or anything like that). The location of the dirt seems consistent - it appears first slightly to the left and right of where the water from the hot tub enters the pool, and then over the course of the next hour, spreads pretty much across the entire bottom of the pool. At the weekend, I will do 2 test cases on Saturday and Sunday and will photograph the results. Saturday will be hot tub only for 1 hour, followed by pool. Sunday will be all pool. I'll take a photo before, after 1 hour, and at the end of the cycle.

2) Chlorination is done via a floating feeder, and I'm using 4-in-1 tablets (chlorine, algaecide, etc.).

3) The main filter is a series of 8 'bags' (sorry, that was the first word to describe them that came to mind - perhaps cartridges is the proper word?) that are set in a circular propeller-type design (when viewed from above). Each one can be removed and is a very fine mesh 'bag' with a tube that connects to the bottom of the filter. They seem to catch a whole lot of silt and fine matter and eventually clog up and need cleaning - I hose each one down to clear all of the muck out of it and put them back in. I wondered if one of these had a tiny hole in it that allowed some finer matter to pass through?

4) Switching from pool to spa is done via a switch in the house. This activates a motorized lever on the valve.

Oh, and one more thing I've noticed - the amount of dirt put into the pool is not consistent. In the first half to full hour of the pump being on is when 95% of the dirt ends up in the pool. If I vacuum the pool (not using the hose vacuum, so none of it is going back into the filter) about an hour after the pump has been running, the pool remains pretty much spotless for the rest of the day.

Thank you for your help with this!

Cheers,
Matt.