Algae in my small pool

[maui19]

I've been a pool owner for 10 years in New England, but recently moved to SC, where I have a small pool with spa (4,700 gals).

Because of the low pool volume, it has been tricky keeping my Cl level where I want it. I have an inline chlorinator that I have to keep almost closed to keep the Cl level down to normal levels.

In the process of trying to find the right setting on the chlorinator, I let the Cl level drop to 1ppm. And then I got some algae spots. Nothing big, just annoying. I shocked to pool to 15-17ppm (for three days), brushed and vacuumed. Everything was fine until I let the Cl level drop to 7.5-8ppm, then the algae starting showing up again. I hate to think I'd have to have a higher shock level and keep it there longer, but that's what I'm leaning toward now.

Data:

CL: 8.0
pH: 7.8
Alk: 90
Cal: 200
Cya: 70
Temp: 86º-90ºF

Whaddya think?

 

[reebok]

it doesn't look like you shocked to begin with. your shock level is much higher than 17. where did you get that number from?
pool-school/chlorine_cya_chart_shock

also, what kind of pool is it?

 

[frustratedpoolmom]

Read Pool School. Then read it again

Your pool is overstabilized from the use of trichlor. This means your CYA is too high.

Refer to the CYA chart for the proper FC levels, if you want to kill/prevent algae, this is what you should follow. I would stop using the pucks and switch to daily bleach additions to maintain the proper levels. Save the pucks for future use when the CYA has dropped below 40, and for vacations, etc.

 

[maui19]

So what to do about the high CYA levels. I'm not wild about daily dosing with bleach. Does anyone use bleach instead of the pucks in the chlorinator?

When we took occupancy of the house (new construction), the pool company had been maintaining the pool for about two months. My first Cl reading came in at 34! Two days later the pool guy showed up, and I asked him what the Cl level was. He said "2" There were 2 pucks in the chlorinator and two in the skimmer basket (I don't even know where to start with that one...). Who knows how long they had been running those high Cl levels, but I'm guessing that's the source of all the CYA.

I ran my pool up north with CYA between 50-70. It was never a problem. That pool took so little maintenance it was amazing.

IIRC, about the only way to reduce CYA is drain and fill--correct?

BTW, this is an inground gunite pool.

 

[reebok]

I asked because your CH is too low for plaster. how new is the pool?
what do you mean source of the cya? chlorine itself doesn't add cya. how are you testing your chlorine?
liquids don't work in a chlorinator. an SWG is the best option imo, or you can use one of these: http://www.ezpool.com/
my cya is 70 also. I just keep my FC at 8ppm. or you can drain some water like you said.
some pools run fine with little maintenance, but that doesn't mean they're sanitized or that you won't get hit upside the head with big problems in the future. some people have good luck, others don't. if you want to make sure you don't have issues, you can follow the advice here. if you want to try it how you've done it in the past or follow pool store advice for your algae, that's fine too, it's your pool.

 

[maui19]

I asked because your CH is too low for plaster. how new is the pool?
what do you mean source of the cya? chlorine itself doesn't add cya. how are you testing your chlorine?
liquids don't work in a chlorinator. an SWG is the best option imo, or you can use one of these: http://www.ezpool.com/
my cya is 70 also. I just keep my FC at 8ppm. or you can drain some water like you said.
some pools run fine with little maintenance, but that doesn't mean they're sanitized or that you won't get hit upside the head with big problems in the future. some people have good luck, others don't. if you want to make sure you don't have issues, you can follow the advice here. if you want to try it how you've done it in the past or follow pool store advice for your algae, that's fine too, it's your pool.

It's a brand new pool, and I'm really not keen on the idea of spending more $$ on more equipment. I don't like running high levels of chlorine. I don't like the way the water smells, and I don't think it is healthy having that much chlorine in the water. I ran my old pool at 4-5 ppm and the water smelled clean and fresh all the time. Of course, I was dealing with water temps that rarely got about 80ºF. Here we're talking high 80s-low 90s all the time, so maybe slightly higher Cl levels is a fact of life.

Right now, I'm going to nuke the heck out of the pool, then drain and fill until I get the CYA down to 50 and see how that works.

BTW, I would never trust a pool to a pool store. That's how this pool got to this point.

 

[anonapersona]

Since your calcium is low now, you can use cal-hypo for chlorine, until your CH gets up. I think that is really useful for shocking a pool when you have room for the CH to rise. You may still need calcium increaser as well. The bottom part of the Pool Calculator will show you the effects on CH of cal-hypo at the doses you need for shocking.

Then you have some choices. You can go to chlorine sources that add CYA -- with the associated drain-and-refill then replenish the other stuff to balance the water required with constantly rising CYA levels.

If that is not what you want, then you can use bleach or liquid chlorine -- with the associated testing and adding chlorine every few days (with the correct CYA you can get on a 2 or 3 day schedule).

If that is too much, then you probably want a SWG but that costs money and it does introduce some chemical effects of it's own.

 

[reebok]

what does the water smell like? mine has a very faint scent of the chlorine jug smell, but only sometimes.
the key is cya. running your levels per the chlorine/cya chart gives you about 0.1ppm free chlorine in the water (chlorine not bound to the cya). indoor pools with no cya have much more active chlorine, and that is where the pool industry came up with the 1-3 or 2-4ppm chlorine level. so in reality the chlorine/cya chart is much more conservative than the pool industry, but the pool industry doesn't take cya into account.
if you drain before you nuke, it will take less nuke. do you have a plan to nuke or are you going to do what you did before?

 

[maui19]

what does the water smell like? mine has a very faint scent of the chlorine jug smell, but only sometimes.
the key is cya. running your levels per the chlorine/cya chart gives you about 0.1ppm free chlorine in the water (chlorine not bound to the cya). indoor pools with no cya have much more active chlorine, and that is where the pool industry came up with the 1-3 or 2-4ppm chlorine level. so in reality the chlorine/cya chart is much more conservative than the pool industry, but the pool industry doesn't take cya into account.
if you drain before you nuke, it will take less nuke. do you have a plan to nuke or are you going to do what you did before?

The nuke is in progress. :lol: Pump will run all night, and I'll do another brush in the morning.

Once I'm done shocking and get the Cl levels back down, I'll start the drain and refill process, which I'll do over a week or so.

My northern pool water smelled sweet and fresh. A number of people commented on it through the years. I think I could get away with running higher cya/lower Cl up there because the temps were so low. I had something like two cases of algae in 10 years and both times I let the pool run out of Cl--and even then it the algae didn't happen immediately.

Here, when the water gets above 10 ppm, the water smells faintly of Cl, but moreover it smells harsh somehow. When I get it back around 7-8 ppm, you can't smell Cl, but I wouldn't say it smells sweet like at my old place.

This pool is interesting. It is small, sunny and warm. The piping/valving on it is much more complex, and I've got a fairly robust Jandy AquaLink that seems cool but I haven't delved into it yet. I'm still on the learning curve here.

Thanks for your help.

 

[frustratedpoolmom]

How are you testing?

When you "smell" chlorine, you have Combined Chloramines, and it actually means you aren't maintaining proper Free Chlorine levels to oxidize the CCs.

You should drain and refill first so you use less chlorine to shock. What are you using to shock? At this point it should only be bleach or Cal-Hypo, and again, I would drain/refill first.

 

[maui19]

How are you testing?

When you "smell" chlorine, you have Combined Chloramines, and it actually means you aren't maintaining proper Free Chlorine levels to oxidize the CCs.

You should drain and refill first so you use less chlorine to shock. What are you using to shock? At this point it should only be bleach or Cal-Hypo, and again, I would drain/refill first.

Actually, CC is zero. I use the test kit from Pool Solutions (been using it for 10 years). I think reebok described the smell perfectly: "mine has a very faint scent of the chlorine jug smell..."

 

[Bob_Funk]

It's a brand new pool, and I'm really not keen on the idea of spending more $$ on more equipment. I don't like running high levels of chlorine.

If you had a salt water generator, your CYA would be perfect & you would only need to shoot for a chlorine level of 4ppm.

Right now, I'm going to nuke the heck out of the pool, then drain and fill until I get the CYA down to 50 and see how that works.

 

[chem geek]

Is the algae yellow/mustard algae that looks somewhat like dirt or dust, tends to grow on the shady side of the pool, and stirs up easily? If so, then this requires higher chlorine levels to kill and if you don't kill all of it then it requires higher chlorine levels to keep away. So by lowering your CYA level via dilution you can more easily attain the high shock level of chlorine needed to kill the algae.

It's also possible that the circulation is poor in the pool and you might try pointing the return in a different direction (perhaps diagonally downward) to improve it.

When you shocked the pool, did you get to a point where the overnight chlorine loss was 1 ppm or less? If not, then you may not have been done killing all the algae even if it was no longer visible.

You are correct that higher water temps have algae grow faster, but chlorine also kills the algae faster at higher temps. Basically, this means that if the chlorine gets too low, things can get out of hand more quickly, but if you stay on top of the growth then usually things are OK. My pool is typically in the 86-90F range, but I have a pool cover on most of the time.

Richard