Juggling High CYA and Algae

[ThisGuy3675]

Hello!

I have a 15K-gal pool. I have only had it in for one year, and apparently messed up on the timing of getting the pool back into working condition (California weather). My CYA has been creeping up since the pool was installed and now its sitting at 100-110ppm. I plan to drain the pool about 50% to lower the CYA. My other issue is that I've accidentally allowed the algae to take off and now I have a green pool. Due to high CYA, and the fact that I'm going to need to drain the pool, I think my approach should be to drain the pool, refill, balance pH, then SLAM. This way I won't need to use copious amounts of chlorine to kill the algae. Once the water is replaced I hope that pH will drop, if not I think I should drop it to 7.4 or so prior to slamming. I'm hoping to get the CYA down to 40 or 50 (something manageable).

The pool is just colored green at this point (nothing major), but the filter hasn't been cleaned since fall. Should I clean the filter before I do all of this and is the above approach way that you all would suggest? I have the TF-100 test kit so I'm ready to do what is necessary.

Also, I have an inline chlorinator which I think is the culprit of the high CYA in the pool. It's adjustable but even when I dialed it back the CYA seemed to race out of control. It has been off since the end of summer and from the end of last year to now my CYA increased 10ppm. What is going on here? Thanks, everyone!

Temp=54F
Cl=0
pH=8.4
TA=110
CH=375
CYA=110
Borates=25

 

[AftonJeeper]

If you can do a partial drain and refill that will save you on bleach expenses. A 50-60% drain should be your goal.

Yes the tablets are the issue, they will continue to drive CYA up. Most people only use those while they are on vacation. You may want to look into buying a salt water chlorine generator (SWG). That way you won't have to worry about pucks or bleach, you still need to test every day or so and add some acid or adjust the SWG output.

 

[peirek]

You are on the right track. Refill and drop pH to 7.2 then SLAM per new CYA level.

How much has the pressure in your filter gone up from clean? We recommend a cleaning after 20-25% increase. If in doubt, you can clean it now but you will also want to clean it after the SLAM has completed.

Yes you will need to make a decision on your sanitizer method going forward
1) Sling jugs of bleach/chlorine
2) SWG
3) Stenner Pump.

The pucks have their place but add significant amount of CYA as you are discovering.

Most all of us here have been exactly where you are at. The only thing you did right it seems is stay away from the Pool Store...... NO ALGECIDES, CLARIFIERS, or OTHER MAGIC STUFF is needed to maintain a perfect pool.

When you get the refill complete post your numbers and we can help guide through the SLAM. Read this carefully and follow to the letter: Pool School - SLAM - Shock Level And Maintain

 

[ThisGuy3675]

@AftonJepper @peirek

Thanks. I removed likely more than 50% of the water and am currently refilling. I power washed the sides and grout on the tiles to remove the top portion of algae on the sides. The pool will likely be filled tonight and I'll start the SLAMMING tomorrow morning. Yeah, the inline chlorinator for pucks is likely to be used far less this summer, probably only enough to keep the CYA up from degradation. Once I get the CYA numbers back post fill, I'll have a better idea how much water was actually removed. Bringing up CYA is far easier than bringing it back down. I got a 1HP sump pump with 1-1/4" line. That sucker removed the 7,000 gallons in about 4.5 hours. Kick rear..

I have an oversized filter (460 sq ft) so I'll probably clean it up after the SLAM process is complete.

I have contemplated the SWG, but it is quite an investment at this time. Perhaps in the next few years I'll install one. I'll just be slinging for a little while. I have a chemical company not too far down the road, which is very handy for muratic acid and 12.5% chlorine.

I prefer this community far over the pool store. Haven't needed to set foot in one yet.

 

[peirek]

And everything here is free or driven to be the lowest cost alternative. Great community and before long you can join the pool snob club!

 

[ThisGuy3675]

Here are my pre-SLAM levels

FC=0.5
CC=0.5
pH=7.5
TA=60
CH=200
CYA=45
Borates=15

I added a little bleach as it was filling up to curb the algae from running away. I added acid last night to bring the pH down. I'm not concerned with CH and TA at this point and the Borates I'll bring up later. The pool is already cleaning up without SLAMMING it but I am going to just to make sure everything is toast. I will update this.

 

[Texas Splash]

Much better CYA. Make sure to lower that pH a bit more (7.2-7.4) before increasing FC with bleach. The rest will work itself out as long as you "maintain" your new FC SLAM level of "20" (based on CYA of 50), brush daily, and follow all the other recommendations on the SLAM page. Good luck!

 

[ThisGuy3675]

I put the bleach in there to get it up to 20 ppm. Lost almost 8 ppm in an hour. Saw @Texas Splash's post added on another 14 oz of acid to bring it down to about 7.4 pH (yep, testing way off). But as calculated it should be sitting right around that.

 

[peirek]

The more often you can measure and maintain the 20ppm FC the quicker the SLAM will go. Multiple measurements and adjustments per day is recommended for the first couple of days.

 

[mknauss]

Be aware that pH tests are inaccurate with FC greater than 10 ppm.

If you test your FC under 10, test pH and adjust it to 7.2

Good luck.

 

[ThisGuy3675]

I found that my FC measurements were not quite accurate. I had 13 ppm again just now. But I thought it didn't seem right. I diluted the sample with tapwater (negligible CL) 50%. So thereby that would make each drop in the TF-test kit 1 ppm. Retested and then I got 18-19 ppm. This seems more correct. Has anyone else had an issue with this? Do you think this would help provide a more realistic analysis?

 

[Texas Splash]

We typically recommend using the 10ml sample (straight pool water) with one hefty scoop of powder. Mix until clear and multiply drop count by 0.5 (standard method). The only test I would try to dilute is the CYA test when a CYA is expected to be extremely high. For FC testing, straight pool water is probably best.

FYI - When using a 5ml pool water sample, multiply the drop count by 1 (used to save on reagent). It's not as precise, but can help in the early SLAM stages. Tough to get an accurate 5ml sample measurement though unless perhaps with a syringe.

 

[ThisGuy3675]

Thanks.

I have been using 10mL with straight pool water, but perhaps I need to add two scoops of reagent powder to capture all the FC. That could be a possibility. I may need to go out and get more bleach before the day is done.

 

[ThisGuy3675]

Nearing the end of day two.

FC only dropping 1-2ppm during the day. The 5mL FC testing helped tremendously (baby medicine syringe-now dedicated to pool). The pool is still slightly cloudy but much better.

I cleaned the cartridge filters and removed as much organic material as I could get at. Looking to run the OCLT tonight. I assume that the pump needs to run during this time as well (will return to a lower speed at 1800 RPM or less). If I don't have a FC loss then do I continue to run the pump 24/7 or can it return back to its normal cycle and slowly clear up the water while the FC drops back down to normal range? I'd like to dial back in my other parameters e.g. TA, CH, and borates.

 

[ThisGuy3675]

Here are some before and during pictures. A nice green tint to the water, but nothing too crazy.

This is Day 2 still at shock level post filter clean.

 

[mknauss]

No reason to run an OCLT until your pool water is clear, really clear.

 

[domct203]

......... The 5mL FC testing helped tremendously (baby medicine syringe-now dedicated to pool). The pool is still slightly cloudy but much better.

I cleaned the cartridge filters and removed as much organic material as I could get at. Looking to run the OCLT tonight.........

Once the water is clear and you do an OCLT, be sure to use at minimum the 10ml sample (1-drop=0.5ppm), even better for an OCLT is the 25ml sample (1-drop=0.2ppm). Using 5ml (1-drop=1ppm) is to coarse a resolution for that.

Keep at it, maintain that FC and that pool will sparkle when you are done. What's clear water? If I throw a coin in my (calm) pool, my 8yo can tell me heads or tails when standing at the top of the ladder (my eyes are too old for that now LOL).

 

[ThisGuy3675]

OK. Got it. Thanks, guys. First time and hopefully last time having to SLAM my pool. I will continue to update.

 

[ThisGuy3675]

Hmmm... last night I tested the FC @ 14.5 ppm and added the appropriate amount to bring it back up around 20 ppm. I didn't test it again as it was near bedtime. This morning came out and tested the FC level at 20.5 ppm. I can see clearly to the bottom, though when the pool lights are on they make a cone of light in the water so still slightly cloudy. Since I got FC right around where I needed it last night and it tested high again, is it possible it is completed? Or should I wait until tonight to get a more definitive answer?

 

[peirek]

I would keep FC @ 20ppm during the day today. Before bedtime do a measurement and note it - do not add anything. Check in the AM before the sun hits the pool. Is the FC within 1ppm? If yes AND your water is crystal clear you have passed.