Question for experienced pool owners - can you explain my experience today with settled green somewhat-non-filterable bottom dust?

[Gary Davis]

I've been in the hospital for a while so I came back to what seemed to be a green-bottomed pool.

But the water itself was actually crystal clear, as shown by looking at the unused hot tub floor.

So I hooked the 90 feet of 1-1/2 inch vacuum hose to the main pump debris canister vacuum.

And I hooked the other end of the vacuum hose to a manual floor vacuum on a 20-foot pole.

And I was pleasantly surprised all of the settled green dust vacuumed up easily with that setup.

But then I noticed the return water (in the hot tub) was kind of abnormally muddy green looking.

Which indicates, to me, the filter isn't catching everything as it's letting some green mud through.
So I emptied the hot tub to take a look at what exactly this fine green mud feels to the hand.

It's kind of pasty. Like super fine clay. Not gritty at all. Kind of like flour between my fingers.

My questions?

Just an explanation from people who have far more experience with green mud than I do.

My first and main question is whether or not it's normal for a perfectly good filter (only a year old!) to allow "some" of the green mud back into the pool?
My second question is what is this stuff that doesn't grow in the water but just uniformly settles down to the walls and bottom.

Is it green algae?

It does NOT grow in colonies if it is algae.
It does not color the water (unless I stir it up).
It simply is a extremely fine dust that settled only in the pool (not in the hot tub).

Any idea what it is and why "some" of it (not much, but some) got through the filter?
Is that normal?

 

[PoolStored]

Perform an Overnight Chlorine Loss Test to rule out algae first, most likely culprit...Link-->Overnight Chlorine Loss Test

 

[sande005]

It perfectly describes an algae outbreak. I spent decades with similar problems before TFP and my SWCG. Green growing patches in places can be sticky and need a bit of scrubbing to remove. Hitting it with a higher dose of CL kills it, and what is suspended settles out on the the sides and the floor (primarily the floor) but is all easily vacuumed up. The water can appear very clear. However, even with care to vac slowly one can kick it into suspension, where it starts to cloud the water. Look for "poofy" clouds as you vac. And some can escape the filter and cloud the water. Eventually, the filter will catch it - but it is better to vac to waste if you can, as you will need to vac more to get it all out as it resettles. You should count on having to clean your filter.

So, since you only use liquid, the supposition is that while you were gone, the Cl dropped too low, and the algae appeared. Then a higher dose was added, which killed of a lot of it (but likely not all). The OCLT will tell the tale about whether there is still live that is consuming Cl. If so, than it is time for a full on course of SLAM.

 

[Gary Davis]

It perfectly describes an algae outbreak.

I guess it has to be algae, as what else could it be since it just showed up while I was gone.
But it's not in the water (unless I stir it up - and then you can't see the bottom).

Green growing patches in places can be sticky and need a bit of scrubbing to remove.

This stuff is NOT sticky. Not at all. It just coats everything with a super fine dust.

Hitting it with a higher dose of CL kills it, and what is suspended settles out on the the sides and the floor (primarily the floor) but is all easily vacuumed up.

As you noted I only use HASA chlorine liquid where I had my wife put in a quart a day which I'm sure she did, but it might not have been enough as when I came back, the floor was green so I had to use the Polaris 380 hooked to a garden hose to vacuum up all the detritus that she allowed to settle in the pool from high winds.

The water is about 62 degrees so with nobody swimming, the dust just settles on the walls and floor.

The water can appear very clear.

The water does appear reasonably clear until I stir it up as I did when I tried vacuuming the detritus with a hand vacuum hooked to a sump pump output to a garden hose.

However, even with care to vac slowly one can kick it into suspension, where it starts to cloud the water. Look for "poofy" clouds as you vac.

Oh yeah. It's poofy all right. it's like a cloud when you disturb it.
That happened when I used a Polaris 380 vacuum to get all the leaves my wife didn't get out of the pool while I was gone so the only thing left was this green dust.

And some can escape the filter and cloud the water. Eventually, the filter will catch it

That's kind of what I was hoping to hear, as I never noticed the filter catching (or not catching) stuff.
I thought the filter was foolproof - but it seems "some stuff" gets back into the pool.

- but it is better to vac to waste if you can, as you will need to vac more to get it all out as it resettles.

Makes sense. But I have no built-in way to "vacuum to waste" that I know of.
The strongest vacuum in this "self cleaning" pool is in the debris canister which is filtered at the main pool pump.

I know most people vacuum from their skimmer ports but my skimmer ports have extremely low vacuum and they're not filtered, which is a long story so let's just not go there as it's different from a non-self-cleaning pool.

I don't have any other form of vacuum that could be open ended.
Do you think it might be inexpensive enough to buy an open-ended pool vacuum pump?

I was thinking of making a vacuum pump out of a sump pump but I gave up on that project as infeasible.

You should count on having to clean your filter.

That's not a problem. I do it all the time.

So, since you only use liquid, the supposition is that while you were gone, the Cl dropped too low, and the algae appeared. Then a higher dose was added, which killed of a lot of it (but likely not all).

That must be what happened. My wife dutifully added the chlorine, but she didn't take care of anything else (e.g., it was filled with leaves when I got back).

The OCLT will tell the tale about whether there is still live that is consuming Cl. If so, than it is time for a full on course of SLAM.

Yeah. I know about it but I have never done it. I've never even "shocked" a pool before as I've never needed to.
The HASA liquid chlorine keeps everything in check where I need at least a minimum of 7.5% of my 30 ppm CYA where I always keep the chlorine levels higher than that.

I'll have to bone up again on the SLAM & chlorine demand theory. Thanks.

 

[Lake Placid]

It’s algae. I see it similarly in pools chlorinated with trichlor. Despite having chlorine, there’s not enough relative to the high CYA level induced by the pucks, and algae forms like that in clear water. SLAM away.

 

[sande005]

@Lake Placid described my history (over decades) exactly. Most of the summer was spent sucking the yellow "dust" out of the pool after a one time "shock" that turned whatever green I had to yellow. Then using magic chems to clear what became very cloudy water. Turn up the amount of Cl injected by the tabs to prevent it. And then repeat in a week or two (at best).
Best money ever spent for anything was a good cartridge filter, and a SWCG. (and, of course, this site and a good test kit).

 

[Gary Davis]

It’s algae.

Thanks. It's green. And dusty. And not in colonies. Not in the water. Only on the bottom. And sides. Very poofy. Very light. It made it past the Polaris 380 vacuum. But not the manual floor pole vacuum.

I see it similarly in pools chlorinated with trichlor. Despite having chlorine, there’s not enough relative to the high CYA level induced by the pucks, and algae forms like that in clear water.

Never used pucks. Only use HASA liquid. I add 30 ppm CYA to the fill water, which means the cyanuric acid level is as low as I can keep it (on purpose).
That way I only need a minimum of 7.5% of 30ppm (i.e., at least 2.5 ppm FC as the absolute minimum) plus some above that of course.
Am considering boric acid (which will reduce that at-least 7.5% to about 5% according to the late Bob Lowry).

Mainly I am considering the boric acid because my high alkalinity fill water (260 ppm TA initially) is costing me an arm & a leg in acid (it's down to about 120 ppm TA at the moment but that took cases of HASA acid).

SLAM away.

There was no chlorine demand so I think I killed it already. I've never needed to SLAM or shock in my life.

This light tan pasty dust that is left over when the hottub dried out must just be the "shells" (or whatever algae have as cell walls).

Thanks for the expert help as I've never seen this green bottom dust until now.

 

[sande005]

If by 7.5% you mean keeping the Cl at .075*30=2 ppm, then that is too low. 2 (or rounded to 3) is the minimum, and any dip below can bring on algae. Even if your helper did it early one morning, and late in the day the next, that could be the issue. You should be traveling at 4-6 ppm (closer to 6 preferable). Even more if your real CYA level is higher than the 30 you noted.

What do you mean by "chlorine demand"? It generally seems to be a pool store term with a very shaky definition. If you referred to the results of passing a true OCLT, then we can agree that all is good.

 

[PoolStored]

What do you mean by "chlorine demand"? It generally seems to be a pool store term with a very shaky definition

We use chlorine demand or FC demand often. At least I do on TFP. It is the daily FC loss when no chlorine is added for 24 hours (or whatever period of time...one day is typical). It will change with seasons, amount of sun and swimmers, CYA LEVEL, use of solar cover, etc. You can measure FC demand by taking an FC measurement, do not add any chlorine, and measure FC again 24 hours later. The difference is chlorine or FC demand.

Knowing your FC demand is very helpful when calculating pump runtime and output % for SWGs.