Water Exchange with Algae

[lblomq]

So I don't remember what excuse I gave myself for not following the experts' advice to do a water exchange in response to my post last August. Maybe I was thinking I would wait until the winter, then got distracted when my wife had a knee replacement, or the wet winter led me to believe I could get by without it, I don't know. Nevertheless, here I am in possibly worse shape with my tail tucked between my legs asking for help yet again. Due to a leak I had to order a replacement part and couldn't run my filter until the parts arrived, and the temperature rose above 100 degrees in the meantime, so here I am wondering whether to SLAM my pool to get rid of the algae I now have and then do a water exchange, or do the exchange with algae present. I'm thinking the latter for the following reasons. According to Pool Math, I need to replace 77% of my water. I have worked out a schedule of how much to drain per hour based on the flow rate of the pump I plan to rent from Home Depot and the fill rate from my tap according to hourly temperature forecasts so I don't expose the pebble tec to air temperature above 85 degrees, and expect the process to take about 26 hours. Based on other posts I've read about water exchanges, my filter won't be running so if I wait until the water exchange is done, I assume it's not worth worrying about any increase in algae since I will SLAM the pool after. The temperature of my pool in the deep end is 82 degrees and my fill water is 78 degrees. Although not much difference, the cooler water theoretically will sink to the bottom where the pump would be, but may also reach the same temperature as the pool water by that time. I don't know if that makes a difference. I plan to start with my attached spa as I can drain that into the pool and refill it separately. Here are my readings:

Attribute	Pool	Fill (tap) water
Temp	82 degrees	78 degrees
pH	7.2 (recently added acid to lower pH and TA)	7.6
Salt	4600	600
CH	1125	250
TA	120	170
CYA	70	0
FC	1.5	0.5
CC	0	0.5
TC	1.5	1.0

Any and all advice is much appreciated and I pinky swear to give strict heed and diligence this time.

 

[woodyp]

Do you have a bottom drain you can use to pump to waste?

 

[mguzzy]

I don't think I've ever seen a procedure for that here.. but my gut would tell me you might want to hit the pool with some chlorine to give it an initial shock.. that way you might kill off some of the Algae before the exchange.. otherwise it will just be a field day for the algae while you are exchanging.. and you are back to the same green mess 26 hours later and you haven't gained anything. that's why a drain and refill works better in that case.

 

[mknauss]

Best with our hot weather right now would be to do an exchange. See Draining - Further Reading
Your salt and CH level would make it a no brainer. I would not bother attacking the algae first.

 

[mguzzy]

Thanks Marty.. I missed the CH levels.. wow.

 

[lblomq]

Do you have a bottom drain you can use to pump to waste?

Unfortunately, no. Although I have bottom drains in the pool, I can't figure out where they go. My main drain setting just empties my spa into my pool.

 

[lblomq]

Best with our hot weather right now would be to do an exchange. See Draining - Further Reading
Your salt and CH level would make it a no brainer. I would not bother attacking the algae first.

The CH is what I was wondering about. According to my SWG manual, the salt level should be a minimum of 4000, so after I do the exchange I will have to bring it back to that level. I haven't had to SLAM my pool in a while, but I assume I can start it the same time I add salt.

 

[lblomq]

Unfortunately, no. Although I have bottom drains in the pool, I can't figure out where they go. My main drain setting just empties my spa into my pool.

However, this made me go look at my pool filter plumbing, and I think I can just set my backwash valve to waste and pump the water out that way. I can then use my pump timer to manage the discharge during the night when it's cooler instead of having to stay up late to manually turn off and on the submersible pump I was going to rent. This would save me time, money and effort. Thanks for the prod to look at this in a different way!

 

[mknauss]

Be very careful using a pool pump to drain a pool. If you lose prime, you destroy a fairly expensive piece of equipment.
A rental sump pump will take about 3 hours to drain your pool if the hoses are properly sized and the effluent point is close by.

 

[lblomq]

Be very careful using a pool pump to drain a pool. If you lose prime, you destroy a fairly expensive piece of equipment.
A rental sump pump will take about 3 hours to drain your pool if the hoses are properly sized and the effluent point is close by.

Thanks for the warning!

 

[lblomq]

I bought a small 1/3 hp submersible pump and did the exchange over 48 hours and it's now done. Here are my new readings:
Temp: 81 degrees
pH: 7.8
Salt: 1000
CH: 350
TA: 160
CYA: 0
TC: 0

The Chlorine/CYA chart article seems to indicate I shouldn't SLAM until CYA is at 70. Am I reading that right?

 

[mguzzy]

You want to SLAM with a CYA around 30, that way you don't have to use as much CL.

 

[IceShadow]

Treat your pool like it’s not a salt pool until SLAM is complete. Once the SLAM is done, then add salt and CYA to recommended levels and turn on the SWG.

 

[lblomq]

I was not expecting this answer so I added salt last night. Does that change what I should do?

 

[DiverGirl1972]

No, you're fine to proceed! The salt level won't affect your SLAM.

 

[mguzzy]

I was not expecting this answer so I added salt last night. Does that change what I should do?

The only thing you really need worry about for a SLAM is prepping the initial CYA and pH, and then maintaining your target FC during the SLAM. Everything else you can pretty much ignore until the SLAM is complete. You need some CYA to protect the FC from the sun.. and the lower the CYA level you can set, the less chlorine you will need to SLAM with per the ever present FC/CYA Levels. Once you raise the Cl to the SLAM target, the pH values are less meaningful because the test is less valid with high FC. So you're more focused on testing the FC only really. So set your pH to 7.2-7.5, CYA to 30 and SLAM away.. and tell us how it goes!

 

[lblomq]

I added CYA yesterday and today (sock isn't big enough to hold all I needed to add at one time) and expect it to be completely dissolved by morning. In a different post Brett S recommended waiting for 24 hours after all the CYA is dissolved and then test the CYA level again to confirm it's at least 30 before SLAMming. The pressure reading on my DE filter has been increasing since I started adding CYA and the needle is now pegged well beyond the max 30 psi mark. Is it safe to run my pump at that pressure until Friday morning? Can/should I backwash to reduce pressure before starting the SLAM?

 

[mknauss]

If you have to back wash, you have to back wash. If you have dissolved the CYA using the sock, you will not lose much.

If you are going to follow the SLAM Process, no need to wait. Start adding liquid chlorine. Assume the CYA of 30 ppm is in the water. Test the CYA level 24-48 hours after it is fully dissolved. Adjust FC or add more CYA based on that test. But start the SLAM now.

 

[lblomq]

The SLAM is going well. My pool looks much better, thank you all. I've been regular in brushing and adding chlorine, which leads to my next question. I've seen the directive to add liquid chemicals slowly in front of a return repeated so many times there must be some reason for doing it that way, yet I haven't come across any explanation why. Before I was a TFP member I broadcast my liquids thinking it was a quicker way to disperse them in the pool. I haven't noticed any negative consequences. What is the donwside to doing so?

 

[mguzzy]

The SLAM is going well. My pool looks much better, thank you all. I've been regular in brushing and adding chlorine, which leads to my next question. I've seen the directive to add liquid chemicals slowly in front of a return repeated so many times there must be some reason for doing it that way, yet I haven't come across any explanation why. Before I was a TFP member I broadcast my liquids thinking it was a quicker way to disperse them in the pool. I haven't noticed any negative consequences. What is the donwside to doing so?

The returns disperse the chems pretty well, that's all. For me in my pool, I tend to put Cl in front of a return in the deep end. Liquid Cl heavier than water and will sink to the main drain to be distributed through other returns.

Brushing is huge... keep it up.