Algae - even though CYA and FC are good

[dd621]

I can't figure out what's going on with my pool and would love to know if I should be doing anything beyond shocking according to Pool School. I recently noticed greenish yellow sediment in the low areas and now have a cc of .5. When we started up our pool it was sparkling clear and 3.5 is the lowest the FC has been this year. Last night FC was 15.5 and this morning it was at 15, still with .5 CC.

Here are my #'s: All measurements are mine except as noted

FC 15
CC .5
ph 7.4 (measured before shock)
TA 210 (I know! We have hard water in our town)
CH 275 (according to pool store)
CYA 32
Total dissolved solids 1200 (according to pool store)

According to the pool calculator, FC of 3 is the lowest it should get - and it got down to 3.5. I am using new reagents, but I'm not really trusting my CYA measurements. At pool opening CYA was below 20 (no reading), I added enough to bring it up 10, it barely showed after five days. I added enough for 10 more and a week later it showed CYA of 40. Now it reads about 32 and if I really study it I can still see the black dot. Pool store readings - which I never believe, were CYA of 125 in their high tech pool water analysis device and CYA of 70 with their tablet method.

More information: Last year we just could not get rid of the algae under the steps. We have the Innovaplas Walkway steps, which do not have openings on the sides. I was constantly shocking the pool (per pool school) and it seemed like we were always waiting for the chlorine to lower enough so we could swim and then it would need to be shocked again. It was very clean at closing with FC of 33 and Polyquat.

In Mid-May it was about halfway full (it lost water through the skimmer because of snow and rain accumulation on the cover). We filled it to mid-skimmer and set the pump up (with new sand) and it has been running about six hours a day. We did not brush it and we left it covered because we didn't want to deal with pollen and birch tree droppings until it was much closer to swim time (pretty late here in Michigan). From peeking under the cover, the water looked very clean and clear. FC was 6 after filling. When FC was about 5 I noticed sediment in the low areas/creases. I was hoping it was sand - FC levels were good and I didn't check for CC. When FC was at 3.5 I shocked it to a calculated 16 but didn't measure it afterwards, and left the pump running 24/7 while we went out of town for four days. We uncovered the pool yesterday when we got home. I scooped out about ten leaves that must have snuck in while we were putting the cover on last year and brushed it. Cloudy sediment drifted up while brushing. The pump is running on schedule, six hours/day. We haven't put the steps in yet. I scrubbed them with bleach, but it is not realistic to scrub every surface, especially since the assembly includes hollow tubes with bolts through them.

So - my questions are:
How should I proceed regarding CYA and Chlorine?
Where is the best place to put the steps (best circulation)? Any other recommendations regarding the steps.

 

[duraleigh]

.5 CC is irrelevant...treat it the same as zero

Keep you FC up for the next few days at 10 ppm or so...not shock value, just higher than normal.

Brush all the sediment you can find just to push it up into the pool water and off the floor.

That might get it all over the next 48 hours, let us know.

 

[dd621]

I've been keeping the FC up and there is only a small amount of gray/brown sediment still in a couple of creases farthest from the skimmer. When I brush I still seem to be stirring up a thin layer of something. Maybe it's just dirt? I'll try the manual vacuum as the automatic one doesn't seem to want to go to the far side of the pool. The water looks clear and sparkly!

FC 9.5
Ph 7.4
TA 80?
CH 275 according to pool store
CYA 25-45????

A couple of other questions - don't know if I should start a new topic or not:

The Ph crept up to 8.0 so I lowered it with Muriatic Acid to 7.4. Interestingly enough, the TA dropped from 210 to 80! It doesn't seem like a half gallon of acid would cause that big of a drop! Does that sound right to you? Could it be because I tested immediately after brushing? Just wondering because I would like to add borates because the water feels "hard" and I want to make sure my TA level is correct first.

Also, I am getting inconsistent CYA readings. Five days ago I was getting CYA of 32 and I could still see the dot if I studied it. Today it tested at 45 the first time and about 32 the second time. I believe I'm being consistent in my testing! I am filling the bottle each time so that the bottom end of the meniscus is at the mark. Does brushing the pool before testing or the time spent mixing the CYA test make a big difference in results? Based on what I'm experiencing with whatever is on the bottom, I'm thinking the 45 reading is more accurate.

I'm also thinking about adding some Metal Free because I noticed that with the light on at night it looks slightly yellow/cloudy. I don't know how to check for metals - pool store doesn't do that anymore.

Also considering adding some DE or cellulose to the filter.

I hope this isn't too much for one posting! I really appreciate your insight!

 

[duraleigh]

You are trying to do too much at once to your pool. Solve one issue, then go to the next.

As of now, I don't think you have solved your problem with dust/dirt/algae on the bottom and your testing seems a bit inconsistent.

Give yourself another day or two with elevated chlorine, vacuuming, etc. and confirm that issue has been put to rest.

DO NOT start new topics. Keep your history in one place

DO NOT put a sequestrant in your water when you don't know if you even have metals. A principle of BBB is not putting things in your pool you don't need.

DO NOT put borates in your pool just yet.

Brush all the sediment you can find just to push it up into the pool water and off the floor.

Keep brushing and vacuuming.

Report back when ALL the debris is off your floor.

 

[dd621]

I think I found the source of the sediment! Our pool steps have a weight which is a cylinder filled with sand. Sand was leaking out when the filter was running! We pulled the weight today and are going to fill it with clean rocks tomorrow. Hopefully that will take care of it! I've been keeping the FC between 5 and 11 (it drops about 5 per day).

Also, my TA reading was off because I used the wrong multiplier! I still want to lower it from 200+ sometime in the near future. I'm still not confident in my CYA reading - but I'm using 30 for calculations.

 

[Richard320]

I think I found the source of the sediment! Our pool steps have a weight which is a cylinder filled with sand. Sand was leaking out when the filter was running! We pulled the weight today and are going to fill it with clean rocks tomorrow. Hopefully that will take care of it! I've been keeping the FC between 5 and 11 (it drops about 5 per day).

Also, my TA reading was off because I used the wrong multiplier! I still want to lower it from 200+ sometime in the near future. I'm still not confident in my CYA reading - but I'm using 30 for calculations.

Steps like that are also a favorite hiding place for algae.