First Mustard Algae Bloom?

[thomearl]

Okay, so i noticed what i'm guessing is mustard algae at the water line in my pool. it's probably in 10 spots around the pool at the water line and then in the corners about a foot below water line. The spots are fairly light and not obvious at first glance, but they are there. I brushed the areas last week and the algae disappated, but it's returned. Do I need to SLAM? Is that the only way to get rid of the algae? I had algae when we first moved into to the house couple years ago, that was taken care by a "pool guy", but this is the first since i've been following TFP.

Here are my numbers from my test this morning.

pH 7.8
FAC 2
CC 0
TA 70
CYA 45

 

[domct203]

What makes you think it's mustard algae?

Right away I notice that your FC is too low, it is well below the recommended minimum for your CYA. This is most likely why you may have algae.

For a CYA of 50ppm (always round up the 'in-between'), your absolute minimum FC is 4ppm, with a daily target of 6-8ppm.

You should get your FC into the proper range and do an OCLT.



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[thomearl]

I guess I don't really know if it's mustard, just assuming cause it's yellowish. Yeah I know my FC is low. I was added chlorine manually for winter and just switched over to the auto system. It wasn't adding enough. Okay I'll get the number up and check out OCLT.

 

[thomearl]

So i did the OCLT test last night and this morning and i passed. Only lost .5 ppm of FC. So now what? Do i just need to keep my chlorine level up and keep brushing and the problem will go away? Couldnt see if the yellow was still there as it was dark when i tested this morning.

 

[Texas Splash]

I brushed the areas last week and the algae disappated, but it's returned. Do I need to SLAM?

Anytime we see the first signs of algae we SLAM. The fact that what you are seeing is so close to the top of the waterline makes me question what it is. Possibly pollen I wonder? Especially since you seem to have passed your OCLT. A few thoughts:
- Hopefully your starting FC for the OCLT was elevated a bit because it was much too low yesterday. The OCLT page states to have a min 3 ppm. If you increased FC higher, that's fine. The important thing is to ensure you have a viable amount of FC in the beginning to evaluate a potential drop.
- Keep in mind that sometimes we can see algae and it hasn't influenced CC or the OCLT (yet). So it's important to confirm if what you see along the waterline is indeed algae. If it is - SLAM right away. Sooner the better.
- Since you showed your last CYA as 45, round it up to 50 and base your FC levels (regular or shock) accordingly as noted on the Chlorine/CYA Chart.
- Sometimes, water circulation is the biggest issue. Make sure those areas you see the substance aren't more stagnant compared to the rest of the pool.

If in doubt, you can always bump the FC to 10 or so for one day (1/2 your SLAM level), brush well and evaluate any changes the next day. If you rule-out pollen and go the algae route, increase FC to 20 and maintain until you pass the SLAM and feel satisfied. Hope that helps.

 

[thomearl]

Yes, I increased my FC to 9 before doing the OCLT. Maybe i'll do it again tonight to double check. But I'm confused, if I'm not failing the OCLT now, how would I know when I'm done with the SLAM?

 

[Texas Splash]

how would I know when I'm done with the SLAM?

Good question. There are times when an algae bloom, either by amount, type, or both, can produce very little CC or expend very little FC. We've had such discussion here before. Perhaps time of day and water temps can also influence this as well. In any case, that's exactly why at TFP we ensure members know that all 3 SLAM criteria must pass. Sometimes water clarity is obscured by dead or dying algae, other times we simply can see small indications of algae (spots, plumes, etc), so we SLAM until we know we've eradicated the algae by passing all 3 criteria.

I mentioned the pollen as a possibility because pollen may not always use-up significant FC, at least not at small amounts. So if you see any of that yellow substance laying around the pool decking, in your skimmer sock (if you use one) or on cars, that could be it. If not, then it may simply be algae. Usually (Mustard Algae) MA remains lower in the shade and places less likely to be disturbed. But if you do SLAM and pass all 3 criteria, you can always increase to MA level just for 24 hrs after the regular SLAM as noted on the MA page. I hope that helps. If you still have questions or concerns, by all means ask.

 

[thomearl]

Want to make sure i have my levels correct if i decide to do a SLAM. Looking at the Chlorine/CYA chart it only lists 3 levels of CYA to do the SLAM at if its a salt water pool. The lowest level listed is 60ppm and even that says not recommended. Not sure why that is, but my level is 45-50. I'm going to need to raise that up to 70 before starting right?

Also, i dont see any detail on keeping the pump running. It only says keep it running 24/7 until done. My question is can i run it at 1/2 or 1/4 speed? Electric rates are pretty crazy here in California, so if i dont need to run the pump at 100% i might a little something left in my wallet after this.

 

[Texas Splash]

I'm going to need to raise that up to 70 before starting right?

Actually no. Leave CYA alone for now which will require less bleach to do the SLAM. A CYA of 50 requires a SLAM FC level of "20". Once you pass the 3 SLAM criteria, THEN you can increase CYA to the TFP recommended range of 70-80 for a SWG pool.

My question is can i run it at 1/2 or 1/4 speed?

Yes. It doesn't have to be cranking at high speeds, just continuous flow to keep the water moving through the filter and stir things up.