dark cloud blowing out when switching from low speed to high?

[RonsPlc]

I have been noticing a dark green? brown? cloud billowing from my return when I switch the pump from low speed to high.
It only lasts about 2 seconds, and seems to disappear in the pool water very quickly. My guage shows everything to be normal.
I don't remember seeing this before, and have been running this pump/filter for the past 3 years.
I changed the sand in the filter last winter, and have SLAM'd the pool this spring (backwashing the filter MANY times).
I have from 0-0.2 CC depending on when I pull the sample, and have 0 overnight loss of FC so I'm doubting that I have algie.

My questions are as follows... Is this normal? Has anyone else seen the same thing? What IS coming out of my return?

 

[Texas Splash]

Good morning! Just to be safe for the crew trying to assist, can you please provide a full set of test results? It might help crack the code on your issue.

 

[RonsPlc]

FC = 8.1
CC = 0.0
PH = 7.5
TA = 100
CYA = 50

Taken less than 20 minutes ago ...

 

[RonsPlc]

We run the pump on low 24/7 due to the fact that we live in the woods, and within 50 yards of a 1.5 acre pond, it helps to keep all the bugs/junk from collecting on the surface.
About the only time it gets turned to high is for vacuuming, backwashing, or mixing in bleach, etc.
My guage is showing the same readings it normally shows after compleating a backwash, but I am thinking that I may just go ahead and try backwashing it again to see if it changes what I'm seeing. I just backwashed it last weekend with the same results, but maybe I didn't backwash it enough. (5 minutes... Rinse... backwash 2 minutes... Rinse... filter on high for 1 minute... switch to low)

 

[RonsPlc]

Has nobody ever seen this, and been able to figure it out?

 

[pooldv]

Sorry, I got nothin.

 

[RonsPlc]

Has nobody ever seen this, and been able to figure it out?

OK... I backwashed, rinsed, backwashed, rinsed, let it run on high for 2 minutes, then swaped to low... will let you all know in the am

 

[keene3b07]

any chance you have an underground leak on the return side? The extra pressure from the high speed might be enough to blow a little dirt from underground, kind of just grasping at straws here.