Green pool after vacation

[barbaranna]

I have been gone for a week,. Pool filter hasn't been run or nothing been done with the pool at the time I was gone. I came back and this is what I found. The ph is slightly low but the chlorine is maybe normal to the hgih side. I did shock before I left for the week. The water is clear not really cloudy but the bottom and walls have green algae all over it. I just came home and started the filter because it was to late to do anything that evening. I really dont know what to do. I know tomorrow I will scrub the walls and I guess the bottom. What I did when I ran the filter this evening is added some ph up to balance. Should I just run the filter tomorrow, or scrub the pool and run the filter, vacum up the algae or shock the pool first. What steps should I take first. I did also add algacide a few days before I left. Its funny because my daughter has been gone the same amount of time, with nothing done to her pool and she has a crystal clear water without any algae. Please help me asap I work long hours and only have Sunday to get most of it done or to at least start it. I am afraid to vacum the green algae because I hear it gets stuck in the filter and if I do it on waste there is alot of algae to get up.

[chem geek]

What specifically is your Free Chlorine (FC) level and also very important is your Cyanuric Acid (CYA) level. The FC reading by itself means almost nothing since the strength of active chlorine (hypochlorous acid) is proportional to the FC/CYA ratio so at higher CYA levels the chlorine may not be effective enough to prevent algae from growing.

Your daughter's pool may have a different CYA level or could be naturally lower in algae nutrients (phosphates and nitrates) or had other algaecide in it (borates, PolyQuat, copper).

If you don't have one already, get yourself a good test kit, specifically the Taylor K-2006 you can get at a good online price here or the TF100 from tftestkits.net here with the latter kit having 36% more volume of reagents so is less expensive per test.

[barbaranna]

ph was about 6.8 fr was 5 alk was about 40 and atablizer showed about 30-50 range

[chem geek]

Since your pH and TA are low, it sounds like you've been using Trichlor pucks/tabs as your primary source of chlorine, is that correct? Even at a low 1 ppm FC per day chlorine usage, Trichlor will increase Cyanuric Acid (CYA) by over 100 ppm in 6 months if you don't have significant water dilution (splash-out, backwashing, rain overflow). Also, your 30-50 ppm range sounds like a test strip reading and they are notoriously inaccurate, especially for CYA. Again, get yourself a better test kit and read the Pool School, especially the article on Defeating Algae.

Your pH may be a lot lower than 6.8 since that's usually the lowest reading in most pool pH tests. So you need to raise that and can use pH Up (Arm & Hammer Super Washing Soda; careful, not the detergent) to do that but don't add too much since you don't want the TA to get too high. You can use The Pool Calculator to calculate dosing.

[barbaranna]

never heard of Arm and Hammer washing soda, I have heard of Arm and Hammer baking soda though. Is that what you mean, if not where do youfind the washing soda. The ph is not the lowest on the strip it is the second lowest. just shows low next to it it shows ok. I have always used these strips and never had a problem. The only time is that I have left the pool unmanaged for the full week, but had no choice.You are talking in a different language than I can understand probably because you understand the pool chemicals and etc more than I do. I just want to know if I can vacum up the algae and then backwash and then possibly shock to kill any left over or what should I do?

[chem geek]

Yes, you can vacuum-to-waste the algae that has settled and can shock the pool with chlorinating liquid or 6% unscented bleach (or Cal-Hypo pre-dissolved in a bucket, if your Calcium Hardness isn't too high).

Arm & Hammer Super Washing Soda is shown here and is usually found in the laundry aisle.

I can guarantee you that your test strips are not adequate. First of all, they don't even measure Calcium Hardness (CH) and can only measure Total Hardness. If you don't have a plaster pool and don't have very hard water, then this can be OK. Test strips also do not measure the water parameters accurately -- drop-based test kits measure to an accuracy of +/- 10 ppm for most tests.

As far as how much to shock, who knows, since you probably don't have an accurate reading of the Cyanuric Acid (CYA, aka stabilizer or conditioner) level. Continued use of Trichlor pucks/tabs increases the CYA level fairly quickly. Even with a low 1 ppm Free Chlorine (FC) usage per day, using Trichlor as your source of chlorine would increase CYA by over 100 ppm in 6 months. That's why it's important to accurately measure it and to use other sources of chlorine as your primary source when possible. Either that or you will need to use an algaecide without fail such as weekly doses of PolyQuat 60 algaecide or use of a phosphate remover, both at extra cost.

[barbaranna]

Thanks for replying. I really understood what you said better this time. What is Cyanuric acid and what does it do to water. I have above ground pool 10,000 gal. Yes, I looked and I am using the tabs like you said.

[chem geek]

Cyanuric Acid (CYA) is also known as stabilizer or conditioner and it is added to pool water in order to protect chlorine from breaking down quickly from the UV ray in sunlight and to moderate chlorine's strength. If there were no CYA in the water, then half of the chlorine would break down roughly every half-hour in direct noontime sun. So you want some CYA in the water, but not too much.

The problem with CYA is that one of the ways that it protects chlorine is by combining with it to form a chlorine-CYA compound. The good news is that this combination does not break down in sunlight (or at least not as quickly). The bad news is that this combination has very little disinfection or algae prevention capability. Fortunately, it takes a very low amount of active chlorine (chlorine not bound to CYA) to kill pathogens and prevent algae growth, but this amount can't be too low. In typical pool water that doesn't have too much CYA, 97% of the chlorine is bound to CYA, 1.5% is a fairly inactive form (hypochlorite ion) and 1.5% is active chlorine (hypochlorous acid) that does all the work.

To prevent algae growth in a manually dosed chlorine pool, one needs to keep a minimum Free Chlorine (FC) level that is at least 7.5% of the CYA level. As I noted in the earlier post, continued use of Trichlor builds up the CYA level so if you don't proportionately increase your FC level, algae can grow faster than chlorine can kill it. At first, such algae growth can look like an unusual chlorine demand and eventually the water turns dull, then cloudy and green. This is exactly what happened to me with my own pool over 6 years ago when I used Trichlor as may primary source of chlorine. After 1-1/2 seasons (11 months) my CYA climbed from 30 to 150 ppm and I couldn't keep up with the chlorine demand. This happened even though I was using algaecide, but I was only using it every other week. Had I not used any algaecide at all, I would have seen this problem earlier, probably in the first year. Had I used algaecide weekly, I could have probably gone another year before seeing a problem. I have a cartridge filter so have no backwashing and used a pool cover pump so didn't get any dilution from winter rains. I didn't know any better at the time.

So first you need to get rid of the algae and to do that you'll need to shock with a lot of chlorinating liquid or bleach. How much depends on the CYA level which is why you'll need to measure that. If the CYA is really high, you'll want to do a partial drain/refill to lower it. The key to getting rid of the algae is physical removal of larger pieces (leaves, algal clumps) either via vacuum-to-waste or scooping it out or filtration and backwashing followed by shocking with chlorine that is maintained at a high level along with 24/7 filtration. Whenever you add concentrated chemicals, including chlorine, to the pool, you will want to do so slowly over a return flow with the pump running. In a vinyl pool, you can also lightly brush the side and bottom of the pool where you add chemicals to ensure thorough mixing. See Defeating Algae for more details.

As for what to do after you get rid of algae, you have choices. You can stop using Trichlor and use chlorinating liquid or bleach as your primary source of chlorine. The main downside to that is that it requires chlorine addition every day or two unless you have a pool cover in which case you can usually add it twice a week. If you want to use Trichlor because it is more convenient, then you need to do something to prevent algae growth. You can use a weekly PolyQuat 60 algaecide or use a phosphate remover, at extra cost. You could also use rains to overflow and dilute the pool water to help keep the CYA levels from getting to high or do partial drain/refill for that purpose.

[barbaranna]

I know you say the sticks are got good in the test strip field but it does have a place which is called stablizer and it is in the range , if that is the same thing.
What I have done so far is I ran the filter and I put in the liquid to clear up cloudiness but when I do that it seems to get cloudy for a while. So I then shocked it and recirculated it for awhile, then this morning when I looked it didnt look as cloudy and ran it all day. When I came home it looks clearer. I backwashed it real good and then I am running it again. The strips say the fc is real high and everything else shows in range. I am doing this alone, I do it for my grandchildren and it is not an easy or inexpensive job. So I am doing what I can financially to keep it up .This probably will be the last year since it is an old pool. So if I stop using the tabs you mean I can just use regular chlorine bleach that you wash with? What and how much would I use. I have always used algaecide along with the tabs and yes it is easier for me but if it about the same expensive, I would use the regular chlorine but dont know how much to start off with. Years ago my husband used liquid from the pool store.Widh I took a chemistry class lol, because it can get pretty confusing but doesnt seem like it for you.

[chem geek]

All I can tell you is that the test strips are particularly bad at measuring the stabilizer level. And since the stabilizer level makes such a big difference in how much chlorine you need, you really should get the better test kit. Even if you get the 6-way HTH test kit from WalMart, that would be much, much better than what you are using right now.

I'm glad things are clearing up. It's primarily the high chlorine level that is helping, along with constant filtration and periodic backwashing. As for how much bleach to add (and yes, this is regular household bleach, but it should be Clorox Regular unscented or an off-brand Ultra bleach), you can use The Pool Calculator to figure out dosages. It will be less expensive than Trichlor because you won't need to add pH Up product regularly. You may need to add some acid now and then, but over time as the Total Alkalinity (TA) level drops, the rate of pH rise will drop as well. If you maintain a minimum Free Chlorine (FC) level of at least 7.5% of the Cyanuric Acid (CYA) level, then you won't need to use an algaecide so will save on that as well.

In my own 16,000 gallon pool (shown here on a somewhat windy day), I only use 12.5% chlorinating liquid added twice a week (I have an opaque electric pool safety cover) with a daily chlorine usage of around 1 ppm FC per day. This only costs me $15 per month. I add a little acid every month or two. That's it. Couldn't be simpler nor much less expensive and the pool remains crystal clear and algae free (in spite of having 2000-3000 ppb phosphates in the water). You can certainly use chlorinating liquid from your pool store as it might be at a decent price, is less to carry, and they may reuse the bottles (better than recycling) as is the case with the pool store I go to locally.

Richard