Is some algae to be expected?

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ndakotaninja

0
Nov 26, 2013
118
Elkridge, MD
I previously had some issues with algae this season (first year owning the pool), but I SLAMed it and cleared it up. It's been a month now and the water is still crystal clear, the FC has stayed at ~6ppm with no issues, CC is around 0, and no dips in chlorine levels from what I've seen (SWG pool). It's a fairly large pool, 17' x 40' x 12.5 (deepest end), and only has 2 return jets. I've angled them to try to get good circulation of the water. I also scrub 1-2 times a week, sometimes more, depending on if I'm outside already to swim.

Anyways, I've noticed that there are spots around the pool that tend to get some small algae growth during the week. Around the stairs (built in) there are some spots that get a little green, when we were swimming a few days ago some of the walls had a very slight slime feeling to them. Some of the nooks and crannies, or chips in the plaster, and in the lattice work under the deep-end ladder, seem to get slight algae growth in them. I focus on these areas when I scrub the pool, but I was wondering if this is normal.

It seems to be in places where the water isn't circulating well to, but the chlorine levels are high enough and the CC has never been more than .5 (the test barely gets enough pink tint to require a single drop to turn it back clear). The scrubbing is supposed to help circulate the water some, and I assume swimming has similar effect as it's getting moved around by people instead of just where the jets send it to. So is there something different I should be doing? Is this normal, as long as it doesn't get out of hand and the chlorine levels stay steady, it's fine? After my previous issues and SLAMing the pool for weeks, I'm trying to avoid having another issue this season.
 
pH 7.5
FC 6.5
CC 0
CYA 50
CH 280
TA 130

I have an in ground spa as well, though I shut it down last month while I was SLAMing the pool (one problem at a time). I am just about to recombine the 2 again, at which time I expect my numbers to change some as the pool water mixes with the fairly fresh water in the spa. It's a SWG pool, so I was going to raise my CYA another 10-20ppm still. Someone mentioned not to bother with the CH as it would require a lot of water replacement. TA is high as well, but again I was told not to bother as long as I kept my pH in check. I'll be doing final chemical adjustments once I get both systems working together again. My FC is also technically higher than it should be for my CYA level, but I was being cautious and figured better safe than sorry and keep it higher to be sure no algae returned.

I've done the full set of checks every week for the last 5 weeks and I've received the same readings every time. My pH got closer to 8 a few weeks back and I used muriatic acid to lower it back down. It's also been fairly dry lately so I've been adding some water using the hose to make sure it stays at the proper level. When doing so, I've turned my SWG up to super-chlorinate.
 
Your ch is fine, don't worry about it. What I'd be concerned of is all that uncirculated water in the Spa. No telling what kinda nasty stuff is lurking in there. Yes, your cya is ok except for the swg part. It really needs to be 70-80.
 
timerguy said:
Your ch is fine, don't worry about it. What I'd be concerned of is all that uncirculated water in the Spa. No telling what kinda nasty stuff is lurking in there. Yes, your cya is ok except for the swg part. It really needs to be 70-80.
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I was waiting to raise my CYA further until I got the spa cleaned back up and working again. Since my FC levels have remained level with the CYA at the level it's at now, it was lower on my list of things to do. And the spa was getting mosquitos in it, but I've since killed them and shocked the hot tub and refilled it, cleaned it, and begun filtering the water.

So if this small amount of algae isn't normal, is it because the FC is somehow too low? With my current CYA level, my FC is also supposed to be lower too, so I feel like it should definitely be killing this stuff. I figured if it's 6.5ppm around the normal circulated parts, and probably higher closer to the return jets, and likely somewhat lower around the less circulated areas (like the steps and nooks), it would still be around 5ppm, which is supposed to be enough to kill algae. I can take some readings of the water near areas I get algae at and test the FC/CC there if it helps diagnose anything.
 
Another oddity that may help knowing, I don't actually know how many gallons are in my pool. I posted my dimensions above, but when I got the pool inspected before I moved in, they calculated it at 25,000 gallons including the hot tub. I used those numbers when I did the SLAM and added in the chemical amounts. I used those numbers when I increased my CYA levels. It seemed spot on because it got my FC exactly to the levels it said it should be when I added the chlorine. If the pool math said "add 60oz to raise the FC 2ppm," I did so, tested it an hour later, and it was exactly where it said it'd be.

So here's the oddity. I started doing calculations of how many gallons the pool should have based on the dimensions (using pool math and just volume calculations, converted to gallons) and it seems closer to 40-42,000 gallons (including the spa). So I'm confused as to what volume is correct. If it's actually 40K gallons, the amounts of chemicals I put in would not have raised levels correctly. If it's actually 25K gallons, why do all the calculations not add up to that?

I originally thought that maybe because of this miscalculation, I hadn't raised the FC enough during the SLAM, except that the tests don't care about pool volume, just ppm of FC and CC, and those all read the proper amounts. So I'm still unsure which calculation is actually right, or if that matters since we're talking about ppm (ratios).
 
ndakotaninja said:
So if this small amount of algae isn't normal, is it because the FC is somehow too low? With my current CYA level, my FC is also supposed to be lower too, so I feel like it should definitely be killing this stuff. I figured if it's 6.5ppm around the normal circulated parts, and probably higher closer to the return jets, and likely somewhat lower around the less circulated areas (like the steps and nooks), it would still be around 5ppm, which is supposed to be enough to kill algae.
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I think you are confusing the SLAM level which will kill algae with the maintenance level which should prevent it or keep it in check but NOT KILL it if it's allowed to start or introduced into your pool (swimsuit, pool toy, ...).
That is the whole reason that maintaining a shock level is necessary to eliminate algae. It's also why you really need to keep above the minimum FC level for your CYA to keep algae from coming back. You may have allowed the stagnant water of the spa to contaminate the pool. Don't know, just a guess where it might have come from.

If using the 25K is what works for doing adjustments I'd go with the 25K.
 
kiss4afrog said:
I think you are confusing the SLAM level which will kill algae with the maintenance level which should prevent it or keep it in check but NOT KILL it if it's allowed to start or introduced into your pool (swimsuit, pool toy, ...).
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No, I've already SLAMmed the pool, killed the algae, added my CYA, and then allowed the FC level to drop back to the normal range. Although, as I mentioned, I've technically not let my FC drop completely to the 'normal' range for my CYA, it's still slightly higher because I was going to work on SLAMing the spa and wanted to make sure I had a buffer in case of contamination. However, it took me a month to get to the spa, and the algae has shown up in the pool during that time.

As to where it came from, I'm not sure. Supposedly keeping my FC at 6.5 should be more than enough to prevent any new algae introduced to the pool to begin growing. The spa water was completely separate from the pool water and never mixed while it was untreated. The algae I've seen in the pool has been appearing for the last 3 weeks or so, and after swimming/heavy rains/etc I've made sure the FC level has remained at 6.5. Which is why I was asking if it was normal to see some small amounts of algae growth, because it's been par for the course with my pool, even with properly balanced/treated water.

And just to point out, the CC has stayed at or near 0 the last month, and the algae I see is very small amounts, but something I still wouldn't expect to see. The pool is pretty old (20+ years), so not sure if it just needs to be resurfaced or something to smooth it out and provide less places for algae to settle.
 
I think your theory about lack of circulation is correct. The FC can drop in nooks and crannies as it fights an algae growth attempt. If the water does not circulate to add chlorine-filled water, the algae will win and grow in those low circulation areas.

How much to worry about it is an aesthetics and effort question. The presence of algae is not a health issue. (It can be a safety issue if it obscures visibility of swimmers, but that is not what you have going on.) If you don't want it there, you will need to continue to brush/scrub it away. Resurfacing will likely help with the algae that is "hiding" in the indentions in the plaster, because chlorine won't be forced into those indentions as easily as passing along a smoother surface.

How often and how long are you running the pump and SWG?
 

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What is your schedule to run the swg? (maybe a timing issue) How often are you swimming (added circulation)?

Working along the premise that is is a circulation issue, I would take a sample from the algae prone area immediately before the swg turned on to see if there is a shortage of FC or higher CC and compare those numbers to those from your normal testing source.
 
I will check when I get home on the exact timings, but I set my pump up to run in the early morning (I think 5am-11am) and then again in the early afternoon (3pm-8pm), giving it about 10-12 hours a day, but not running during the 'peak' hours for my electric bill. I'm still trying to balance the correct SWG % with the right amount of runtime to keep my FC balanced. Right now, as I said, the FC is staying high, so I've been slowly dropping my % output. The next thing I can do is adjust the runtimes. Been busy, so only swimming about 1-2 times a week in the late afternoon/early evening, while the pump is running.

I have taken water samples right next to algae spots and tested those and it seems to be in the 6-7ppm range, even during mid-day, sun is out, and pump isn't running, so I wasn't sure how it would be growing and assumed it normal.
 
If you have green in the pool, you have, or have had a lack of proper FC at some point or points. There is no other explanation, there is no argument. The ONLY thing that allows Algae to grow is a lack of proper FC.

You may never have killed it all with a correctly done SLAM procedure, but whatever the case, this is the reason. Once you kill it all, and keep the FC correct ALL the time, this problem will go away. If you relent and let it slip, you will have Algae return to your pool.
 
The only way that could be the case, Brushpup, is if the test kit wasn't giving me correct readings. Since I've SLAMed the pool (according to the SLAM guide and with no visible algae showing, and cc at 0), the FC has remained at or above 6ppm. It technically should be lower since my CYA is also lower right now, but since I was also seeing algae appear again, I didn't want to let it get too low.

The only thought I had was my pH has been higher than usual (7.8-8.2 or so), and I started lowering it with muriatic acid, and it's now down around 7.6. I've also noticed a lot of new staining on the pool that's a dark metallic (almost green) color that I first thought was algae. I thought maybe the high pH caused the metals in my heater to get into the pool and cause the stains, wasn't sure if it'd have any effect on algae growth.

The algae that I'm seeing is in the nooks or crannies, like on the stairs, that may not get direct chlorine, but again, even in those hard-to-reach places, I've tested and it's still over 5ppm FC, which should be enough. And to go with that, the cc has been <.5 or 0 ppm for the last 6 weeks, during which time the algae has grown. It's not very obvious, it dissipates when I scrub it, only to reappear a few days later in the same spots.
 
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