Pool Draining and possible black alge

[Jurate1]

Hello all, as you previously recommended I have been postponing partial drain of the pool due to heat but am now thinking I should just do it if I can safely. It has been 116 in Tucson lately. Temp does not drop below 85 until at least 9 pm at night. I need to drain apx 1/2 of an 8000 gallon pool. I found a previous post that recommended this method... Also numbers are slowly coming down due to evaporation but not quickly enough

Is this correct...
Rent sump pump
Turn off pool pump
Place in Deep end of pool begin draining at 9 pm
At the same time put hose in pool at the shallow end of pool. Let it go all night.
Temp of pool and temp of water from hose is about the same 88 degree's.
It took 1.25 seconds to fill 1 five gallon bucket of water from hose

Will the sump pump drain quicker than the hose can refill??
In the morning by 10 am temp is above 85 degree's..
If needed here are current numbers FC=7.5, TC 7.5, CA 275, TA 70, CYA 100, PH 7.2... I did add more chlorine today. But it is getting time consuming trying to keep it a 8 or higher...

The pool looks good, however I did note some dark spots on the pool floor. See attached. I don't know if this is just discoloration of the pool floor from the muriatic acid or chlorine? or possible Alge. My husband reports he was not able to get any scrapings and he thinks it is just discoloration. See attached.. It is the dark discoloration near the pool drain... Pool is nice and blue not green as it appears in picture. This is just shadow from sun.. Any advice is appreciated. Thanks, Gina

 

[LoneWolfArcher]

According the CYA/FC chart Chlorine / CYA Chart - Trouble Free Pool

You should be keeping the FC above 11.

Hopefully it is not black algae because it has deep roots in porous substances (like plaster/concrete). 3 years ago I was having black algae due to my CYA being too high, but lucky I have fiberglass so brushing it would kill it with a FC in the right range.

 

[mknauss]

Read the Exchange in Draining - Further Reading

 

[Jurate1]

Thanks Lonewolf, I was keeping it at the minimum 7-8 but if I should shoot for 11 will this damage the surface of the pool? I have a Pebble tech surface... Also I have just been pouring it in about 1/4 gallon at a time. But if I need to add even large amounts almost daily should I dilute prior to pouring in to prevent any damage? I usually add in early morning so pool can run all day..
I have read the draining posts. I guess I am just looking for reassurance from someone on the forum who has done this successfully without any damage.

 

[LoneWolfArcher]

Thanks Lonewolf, I was keeping it at the minimum 7-8 but if I should shoot for 11 will this damage the surface of the pool? I have a Pebble tech surface... Also I have just been pouring it in about 1/4 gallon at a time. But if I need to add even large amounts almost daily should I dilute prior to pouring in to prevent any damage? I usually add in early morning so pool can run all day..
I have read the draining posts. I guess I am just looking for reassurance from someone on the forum who has done this successfully without any damage.

Is it a new pool or replaster?

 

[Jurate1]

Hello everyone, so I took the plunge today and drained I would say about 3/4 of the pool. The pump I had was very quick. It only took about 2 hours. It was a cooler, cloudy day today with rain in forecast so I went forward. I am now refilling with 2 hoses. Once it is filled do I just do the routine testing again and add chemicals based on those results? Should I run the pool for awhile before doing first testing? Thanks, Gina

 

[Jurate1]

It is not a new pool. It is about 14 years old. It is Pebble tech. I made no changes just drained/refill.

 

[mknauss]

Once it is filled do I just do the routine testing again and add chemicals based on those results? Should I run the pool for awhile before doing first testing?

Once full, run the pump and brush the pool to mix the waters well. Then take a sample and run a full suite of tests. Adjust as necessary for Recommended Levels

 

[LoneWolfArcher]

It is not a new pool. It is about 14 years old. It is Pebble tech. I made no changes just drained/refill.

You will be fine then up to SLAM level for your CYA (which will be pretty low initially with a drain and fill).

 

[Jurate1]

Good morning everyone. I just ran all the tests on refilled pool.. Results FC 5.5, PH 7.5,TA 110, CH 150, CYA 40
CSI-39. I believe everything looks good but I have questions...
How can FC be 5.5 when I have not added any chlorine yet?
My hardness is low. Calculator says to add 22 lbs. of Calcium chloride... Is this really necessary??
Alkalinity slightly high...

 

[Flying Tivo]

What are your Fill water numbers?

 

[Jurate1]

The numbers posted above are after the fill...

 

[Jurate1]

Results FC 5.5, PH 7.5,TA 110, CH 150, CYA 40
CSI-39.

 

[mknauss]

The numbers posted above are after the fill...

They are asking the pH, CH, and TA of the water you use to fill the pool. Because of evaporation, if that water has high CH, your pool water CH will rise over time.

 

[Jurate1]

Oh I see.. Water from tap: PH=8.2, TA=100, CH=0, CL-0

 

[mknauss]

You filled with softened water. Is that your plan going forward for your make up water?

 

[Jurate1]

We just purchased this home and it does have a water softener. I guess we did not realize it also was for the exterior plumbing as well.. But yes we would be using the softened water for fills..

 

[mknauss]

OK -- with that, yes, you need to add calcium. Get your CH up to ~300 ppm. 10-12 pounds of calcium chloride will work.

Or, use Calcium Hypochlorite to chlorinate the pool with until your CH tests at around 300 ppm,

 

[Jurate1]

Thanks everyone for your assistance. I hope now I am on the road to just routine maintenance...