Pebblecrete (Plaster) Stains (or dirt?)

[amlez]

Not sure where to post this - pretty sure my problem isn't algae or mineral staining (I've performed both chlorine puck and vitamin C tests with negative results).
I've got brownish stain covering all submerged surfaces of the pool (wall & floor). The puck & vitamin C tests made no impact whatsoever on the 'stains'. 'Normal' brushing with a pool brush on extendable pole makes no impression on the discoloration. The only way I can clean it is with a very stiff bristled hand brush, and quite a bit of 'elbow grease'.
Below is a sample of an area I've cleaned in the swim out (top left corner of pic) :-



The pool is maybe 18mths old - this issue started occuring maybe 6 months after it was filled, and seems to be getting gradually worse.
The pool builder (who it turns out was a bit of a 'cowboy' - and we no longer have dealings with) , suggested we would need to continually ( a few times a year) scrub the water line as the white finish we chose would show a dirt line at water level, but we didn't anticipate having to scrub the entire pool surface!!
When the discolored areas are scrubbed, a noticeable brownish 'cloud' rises from it.
Any ideas on why this is occuring, and how best to treat it, short of donning the scuba tanks and having to manually scrub the entire pool?

 

[ajw22]

Do you have one of our recommended test kits?

Post your test results.

Do a Overnight Chlorine Loss Test

 

[amlez]

Not sure current test results will explain an issue that's appears to have been ongoing for quite some time - in fact test results from 12 months ago may better explain the issue if it is one caused by unbalanced water ??

In answer to your question tho, yeah I use the Aussie CCL kit - testing from 2 days ago :-

Chl 6.5
pH 7.6
TA 75
CYA 45
CH 350
Salt 3000

These are quite irrelevant to the posted issued however - you see it's our monsoon season ATM and we've had over 5 inches of rain in the past week and clearly there's some dilution of chemicals.

Results from last week (before the rain) :-

Chl 7
pH 7.8
TA 85
CYA 60
CH 380
Salt 3800

Testing over the past 7 or 8 months since I've had the test kit have all been pretty well around my parameters, and the pool water quality/clarity has been nothing but exceptional in that time.

 

[ajw22]

Turn off your SWG for a night and do a Overnight Chlorine Loss Test

What are your pump and SWG run schedule?

 

[kimkats]

Well that picture is quite telling. So you are saying it will come off when you hand brush it with elbow grease...............there has to be something in the water that is causing this. That is why Allen is pushing you so hard on the water test results and such. This is going to be a puzzle and we need all of the pieces to get the full picture.

I hear what you are saying that is started a long while ago so lets go back to then. Do you keep records of what is added to your pool each time?

Your water-how was the pool filled to start with? How do you add water to top it off?

I am sure there will be many more questions we come up with but in the end we might be able to figure this out.

Kim

 

[amlez]

Thanks Kim

I hear what you are saying that is started a long while ago so lets go back to then. Do you keep records of what is added to your pool each time?

Yep - keep a spreadsheet of everything that has gone in since startup - costs, test results, etc - I'm a bit anal like that

Your water-how was the pool filled to start with? How do you add water to top it off?

Filled with my household tap water at startup, and top up also from tap water (unless it's monsoon season like now and top up comes from the heavens).

I am sure there will be many more questions we come up with but in the end we might be able to figure this out.

Yeah, I hope so - not keen on spending months of scrubbing it clean only to find it reoccur.

My guess though is that this won't happen - I'm hoping this is the result of a very poor startup/handover by the dodgy pool builder.

The only chemical addition (to my knowledge) he input was the original salt.

After quite some time (certainly weeks - maybe a month/month & a half while waiting for PB to return??) I got a store test done to find it was basically devoid of CH & CYA - had to put 50kg of calcium chloride in over a 4 week period

I had no instruction to brush the pool during startup phase (which I googled might be a requisite??), etc, etc

So, I'm hoping that once cleaned, it won't reoccur - but curious as what's caused it, but more importantly hoping to find a more automated cleaning procedure than elbow grease (I wasn't joking about having to don the scuba tanks )

 

[kimkats]

Brown dust-lets talk about this some more. Does this happen ONLY when you scuba down and hand brush it up? Does it dust up at all when you brush the regular way with pole and standing up?

I am SO glad you are where it is warm now for this next one----dive down and feel where the clean line meets the "dirty" line. Use your fingernail to see if you can feel a ridge or such as well. Use your mask to get a good look at it.

Do you have a pool store that can do a metal test? I know you said the vit c and chlorine tablet did not do any good but I don't want any stone left unturned for this puzzle.

Filter-have you looked inside the filter? What does the sand look like? Do you know what kind of sand they used (grasping at straws here but....better safe than sorry)

Lets talk about your plaster start up. Do you know if they did an acid wash after the plaster was put on but before the water went in?

Make sure to keep a good log of what is going on. Dates with what you did and what happened so we can keep track of what is what.

Kim

 

[amlez]

Brown dust-lets talk about this some more. Does this happen ONLY when you scuba down and hand brush it up? Does it dust up at all when you brush the regular way with pole and standing up?

Just to clarify - haven't donned the scuba gear yet (& hope not to have to). I've worked around the entire wall at about 300ml from waterline, and started to attack the swimout in order to get a pic to post here. Completing scrubbing the swimout won't be such a big deal, but obviously once I get to the stage of having to 'go under' (lower walls & floor) things will get exponentially more difficult.
Re 'brown dust' - regular vacuuming is via a robo cleaner usually twice weekly. While it climbs walls and spends some small time in the swimout, my practice is to 'pole brush' the swimout every 3rd or 4th robo clean in order to push leaf litter, palm berries, etc, to the main floor where robo better handles it. When performing this brush, there is a quite a cloud of dust that raises. When brushing the main deep floor, I hadn't noticed as much dust raising, but perhaps that's due to the added depth and it not being so evident, or that the robo is vacuuming this floor area more proficiently.
The more I think about this, perhaps this is the issue. We do live in an environment that is quite dusty (particularly in our 'dry' season) - the better half is constantly complaining about having to dust every week. I hadn't extrapolated this to the pool, and perhaps there is a constant input of dust into the pool that over time has 'absorbed' into the porous pool surface? I'll be the first to admit that my manual brushing of the pool hasn't been overly great. While I understand the robo doesn't pick up all fine dust, I do 'manually' vacuum every 2nd month or so, and generally give the floor a brush the day before manually vacuuming. Not sure this would account for 'airborne dust' settling on the walls tho ??
Could this be the issue? - is it a 'common' thing for plaster/pebblecrete surfaces to 'absorb' airborne dust introduced to pool water?

I am SO glad you are where it is warm now for this next one----dive down and feel where the clean line meets the "dirty" line. Use your fingernail to see if you can feel a ridge or such as well. Use your mask to get a good look at it.

Definitely no ridge or difference in feel from cleaned to uncleaned surface.

Filter-have you looked inside the filter? What does the sand look like? Do you know what kind of sand they used (grasping at straws here but....better safe than sorry)

No. Wouldn't think this would be an issue - pool only maybe 18mths, and I regularly backwash.

Working from memory here, but pretty sure filter medium is cristallite?

Lets talk about your plaster start up. Do you know if they did an acid wash after the plaster was put on but before the water went in?

Yep - acid wash was performed.

 

[kimkats]

Sounds like there could be a couple of things going on.

-dirty/dusty area as seen by having to dust often inside. This can be helped by a couple of things:
-Lets work on your returns-throw some ping pong balls into the pool to see the water movement. The balls will show you if there are any "dead" areas in your circulation pattern. Also look at the leaves and such at the bottom of the pool. Do the leaves just sit there or are they moved around by the water flow? You can influence this with your returns as well. This will help get the dirt/dust up and into the filter.

-filter-I do not know of "cristallite" as a filter medium but am guessing it might be some sort of glass instead of sand. I will tell you that many people have found they do not have good luck with the glass type of filler. Sand is better at getting the smaller stuff especially if you add some DE to it to help it filter down even smaller. Just something to think about.

On dirt embedded in new plaster-I am not sure this could happen after 6 months or so. It has happened when some dirt got onto some brand new plaster that did not have water in it yet and was not washed off or cleaned right away. I don't think it would happen this far out.

I would like for you to do a OCLT as seen here: Pool School - Perform the Overnight FC Loss Test (OCLT) This will help us rule out this being dead algae dirt even though we both know it is probably dirt BUT why is it sticking????

Another thing you can do is do a couple of days of SLAM level as seen here: Pool School - Chlorine / CYA Chart use the shock levels for you CYA. I am hoping this might help with the dirty look.

Kim

 

[amlez]

Thanks Kim,

Did OCLT a few days (and a month ago, and 3 months ago, ......) - all return zero overnight loss.

I guess I'll just continue to scrub away, and be more diligent with brushing and see if the cleaned areas remain clean in 6 months.

 

[ajw22]

Thanks Kim,

Did OCLT a few days (and a month ago, and 3 months ago, ......) - all return zero overnight loss.

Confirm that you turned off your SWG when you did the Overnight Chlorine Loss Test?

 

[amlez]

Yeah - SWG/pump runs around 8 hours daily - off at 5pm ...... comes back on mid morning

 

[duraleigh]

Your words and your picture makes me think it is iron. You said you have done the vitamin C test for iron but I think I would do it again. Can you feel a difference in the cleaned area and the stained area? If not, that further suggests iron staining.

Have you tested at a pool store for iron? If not, test both your pool water and your fill water and report those results. Also, when you do the vitamin C test, how long are you allowing the container of vitamin C to touch the pool surface?

 

[amlez]

Thanks Dave.

Your words and your picture makes me think it is iron. You said you have done the vitamin C test for iron but I think I would do it again. Can you feel a difference in the cleaned area and the stained area? If not, that further suggests iron staining.

I've done the vitamin C iron test 1/2 dozen times over the past 2 or 3 months in a number of different ways (tablets crushed in sock, tablets rubbed on surface, tablets place under lead weight & allowed to dissolve) - all come up with no noticeable effect.

Have you tested at a pool store for iron? If not, test both your pool water and your fill water and report those results. Also, when you do the vitamin C test, how long are you allowing the container of vitamin C to touch the pool surface?

Haven't done pool store iron test - I'll give that a go during the week.
Vitimin C left on pool surface over an hour (& up to 2 hours when in the sock - until fully dissolved basically).

Just on another matter - as the thread title suggest this is a 'pebblecrete' pool. Since I've been visiting this site I've come to believe that what us Aussies call a 'pebblecrete' pool, you guys over there class as a 'plaster' pool, but then recently googled an article that suggested there is a difference.

Not sure if this is of any substance in relation to this issue - but to be clear, my pebblecrete surface is quite 'rough' (although not as coarse as many pebblecrete pools in the region as I elected to go with a finer aggregate/pebble).

 

[duraleigh]

well, I am stumped. Stains are either inorganic(vitamin C test)or organic (chlorine test). I don't know of ANY other category.

 

[kimkats]

Dave add in that he CAN scrub it off with some elbow grease?? I am hoping it is just that his area is very dusty. Then once he gets the "embedded" dirt up and out then makes sure his circulation and filter is spot on I am hoping this will not happen again.

 

[duraleigh]

Dave add in that he CAN scrub it off with some elbow grease?? I am hoping it is just that his area is very dusty. Then once he gets the "embedded" dirt up and out then makes sure his circulation and filter is spot on I am hoping this will not happen again.

Yeah, I agree. The only mystery with that is he reports a somewhat regular (but not enough, really) cleaning cycle that should have precluded any embedded dirt