My turn to tackle algae

[cornercarver]

Hi all. New to the forum and need some guidance. I read as much as I could as an unregistered guest.

Typical green algae/cloudy pool. I have started with liquid shock and have gone from green to steel blue and cloudy. I can see down about 18"-24".

18' x 33' oval approx. 15,000 gals
above ground with vinyl liner
sand filter hayward pump

I am using the HTH 6 way kit

Chlorine - 0-trace
pH - 8.2+ (as high as it would read)
TA - 100 ppm
TH - 80 ppm
CYA - 0

Based on my reading, I need to lower pH and shock. I used the pool calculator to determine I need 4 gallons bleach and the calculator gave me amounts of acid to add based on delivery method.

My first question is does it matter which order I add chemicals? Do I tackle pH then go after the Cl or vice versa or does it matter? From other threads it looks like starting with shock is the first order.

My second item is that I struggled all last year keeping Cl levels up. I just used strips to test and eyeballed clarity. I had a few algae issues but it wasn't really a struggle but I know I need to keep my CL levels up. Based on my reading of the forum, after I get the Cl and pH working, I can use stabilizer to get the CYA up. Am I on the right track?

Thanks!

[aylad]

Hi cornercarver, and welcome to the forum!

You are on the right track--the key to clearing the algae is going to be achieving shock level (12-15 ppm for a 0 CYA pool) and then maintaining it until the pool is clear and you don't lose more than 1 ppm of chlorine when measuring at night and again in the morning before the sun hits the pool (that way you're measuring actual chlorine use in the pool, and don't have to guess at how much was lost to sunlight). That being said, anytime you have high chlorine levels, you're also going to have falsely high pH readings. So...I would use the acid to lower the pH into the 7.0-7.8 range first, and THEN shock the pool.

Typically we would recommend that you leave the pump and filter running 24/7, backwashing the filter as your pressure gauge indicates, but can you tell me what size pump and filter you have? If the filter is over-driven by a pump that's too large, which sometimes happens in AG pools, the pump can actually push the algae through the filter and back into the pool, except in smaller pieces.

Regarding your test strips, I'm hoping you've realized that they're not very reliable, and that's why you're using the 6-way kit, which is actually a relabeled Taylor kit. You're right in that you can add stabilizer to the pool to raise your CYA, but I would get the pool cleared up first.

[cornercarver]

Not sure what parameters you're looking for...

Effective filtration area - 1.7 ft2
Filtration rate - 20 GPM/ft2
150 lbs sand

pump - 1.5 hp

[Sean OBrien]

Falling back on my engineering knowledge due to my lack of pool knowledge...

You will need to find out what the flow rate is on your pump and check it against your filter. In this case your filter has an effective filter area of 1.7 ft2 and a filtration rate of 20 gpm per ft2. Little basic math should translate that to the filter being able to handle 34 gpm.

Considering that your pump is 1 1/2 HP - you are probably looking at somewhere between 75 and 100 gpm flow on the pump (depending on head and line loss...though the end result will be the same). The end result is that either your filter is too small or your pump is too big.

Now it starts to get a bit fuzzy on my experience with pools... As I understand it, you want to filter your whole pool once every 8-10 hours. So, your pump is close to being the right sized (if my assumptions are correct), however your filter seems to be about half the size it should be.

That results in the water being forced through the sand bed too fast, and when it moves too fast things like algae just get shredded by the sand and ejected back out into the pool as opposed to remaining in the filter where they can be removed by backwashing the filter. And that can mean that while you manage to kill the algae, the dead particles remain floating about in the pool until you manage to sort out the filtration of those solids from the pool itself.

[cornercarver]

So, I got my pH to 7.2 yesterday and then shocked with bleach yesterday evening. Chlorine level appeared to be 10+ppm using strips (my HTH only measures to 5). Checked chlorine this morning and had 1 ppm using th HTH kit. pH still 7.2.

I discovered that I had calcium scale on my liner as a resulot of my high pH over winter. The water is now very cloudy. I'm running my filter and I think I'm making progress. My pressure gauge isn't working so I am observing water flow to determine when to backswash. I'll get a new gauge on soon so I won't be guessing.

I filled a small glass with pool water to see if the white stuff would settle overnight. The white particles were still in suspension this morning. Am I still dealing with dead algae or also calcium precipitate? When do I go nuclear and use floc?

Also, the kids are dying to jump in the pool. Is it safe for them to jump in for a bit in this condition? I don't want them swimming for long but a few minutes in will make them feel like progress is happening. At least this project has the youngest interested in pool maintenance. He's been using the skim net and helping with the water testing.

[aylad]

Here is a link to a prodecure you can use to make your hth kit read higher chlorine levels... http://www.poolforum.com/pf2/showthr...a-good-testkit)

If you lost that much chlorine overnight (assuming the 1 ppm reading was before sun hit the pool?) then you still have a good ways to go in killing off whatever is in your water. If it was after the sun hit the pool, then we don't know if it was due to oxidizing goo, or to sunlight. If you'll test at night and the next morning before the sun is on it, you can compare the numbers and get a better idea.

Your calcium level is not high enough that I would expect calcium scale, but I could be wrong--can you flake off a piece of it, put it in a covered jar with some vinegar overnight and see if it dissolves?

I would not use floc at this point--you need to make sure that you've killed off all the living algae, and filtered out what you can before you even go that route, since if not used carefully it can create other problems for you.

Regarding swimming, as long as the pool has chlorine in it and the pH is within range, the biggest danger is going to be swimmers underwater in cloudy water so that you can't see if one of them is in trouble or not. If you can't see the swimmers, I wouldn't let them in.

[PoolDoc]

1. Brush your pool completely, to make sure you don't have any hidden algae left.

2. Wait 4 hours. If you have no green after brushing, still have good chlorine levels and OK pH, it's safe to swim from a sanitation point of view. What's NOT safe is the cloudiness: it only takes a few minutes (occasionally, 30 seconds) of submersion and a person can no longer be resuscitated. So if you let your kids play, WATCH them, and maintain a running head count, because you will NOT see them on the bottom in time!

3. Floc is unpredictable. If you want to try it, order some PAC (poly-aluminum chloride):

GLB Pool & Spa Products 71408 1-Quart Drop n' Vac Pool Water Clarifier @ Amazon

but then use the white bucket test to make sure it's gonna work, before you dump it into the pool. This is one case, where a little 'too much' may be better than not enough, so you may want two bottles.

However to use floc, you will EITHER need to vac to waste OR make SURE your filter is working well, and won't blow the floc THROUGH the filter. (If you have a low speed, that will work, if the filter is full of sand.)