How much chlorine is required please?

[Caesar]

Hi,

We have 2 freshwater in-ground pools. Both are tiled. One has 400,000 Liters, the other one 480,000 Liters (they are side by side).
The pH is 7.6 but we have to add every day at least 2 liters of acid into each pool to maintain the pH at that level.
I added bicarb to raise alkalinity, but that raised the pH dramatically. So adding acid again brought down the alkalinity again. It is like a dog running behind it's tail.
Maybe someone has a tip how to get the alkalinity to 100 while maintaining the pH at 7.5? Currently the alkalinity is at 30.

My other question is how many liters of liquid chlorine should I add every day? At the moment we are adding 8 liters into the 400k Liters pool and 9 Liters into the bigger one (done every night). Is that sufficient?
The pools are getting brushed and vacuumed every night too.
We are very close to the equator so water temperature is constantly 29°C.

Thank you for any help.

Cheers
Caesar

 

[Hawk]

Take a look at the Pool Calculator and see if it helps you.

http://www.poolcalculator.com/

 

[woodyp]

Do you have a SWG or any water features? Welcome!

 

[jblizzle]

Welcome to TFP!!!

Baking soda (sodium bicarbonate) should raise the TA, but have very little impact on the pH. You can use PoolMath at the bottom to get an idea. Is there a reason you are trying to maintain a TA of 100? There is no problem being lower than that, although 30ppm is a bit low. I would suggest getting it up to around 60ppm and see how the pH behaves. When the TA is too high, it will tend to drive the pH up.

Is there a lot of aeration in the pool? Water feature, spill over, etc? That too will drive up the pH.

The amount of chlorine required is a function of sun exposure, use, and your stabilizer (CYA) level. Also we would need to know the strength of your liquid chlorine. It is normal to lose 2-3ppm of FC each day just to the sun when the CYA level is appropriate. If you have none or higher bather load, the daily use could be more.

Please add your pool details to your signature and location to your profile as described HERE as it will help us help you.

 

[Caesar]

Hi,

And thank you for the welcome greetings, much appreciated.

I'm in North East Brazil (Fortaleza).
It is very hard to get your hands on chemicals here and we need to improvise. I can't tell the concentration of the chlorine. But it seems to be similar to the chlorine I had DownUnder.
The pool test kit states alkalinity should be between 80 to 120 so I took 100 as an average value. But if 60 is ok too, then I'm happy to go with that value. But I assume I need to lower the pH first? Or is it normal for such size of pools to add 2 liters of acid every day? We have around 20 swimmers in each pool every day and all of them are wearing sun screen (which is washed up on the boarders every evening).
When I was in Australia, I added "sun screen" to reduce the vaporization of the chlorine. I don't know what product to get here in Brazil which has the same effect.

There are no water features or spills.

Again, thank you for any tips and ask questions if I missed anything.

Cheers
Caesar

 

[jblizzle]

Read these in Pool School to get a better understanding of the chemistry:
ABCs of Water Chemistry
Recommended Pool Chemicals
How to Chlorinate Your Pool

We mostly deal with residential pools, so I am not sure what would be normal for acid use and chlorine use for your pools (is this a resort?). But, the chemistry is all the same.

Cyanuric acid (CYA) is what is needed to protect the FC from the sun. You need to know what your level is (and of course whether the regulations there allow it to be used in a public pool) and that will help determine how much chlorine is required.

You need to test the chlorine level everyday to ensure you are adding enough to counter the loss to the sun and the bather load (all the sun screen does not help).

I would kind of be surprised if the amount of chlorine you are adding is enough. That is only around 2-2.5ppm of FC in each pool and your use is higher than residential pools.

I would suggest adding the baking soda to get the TA to around 60ppm (it would be 21 kg to raise the 400k pool from 30 to 60) and this will only raise the pH by 0.06 ... so hardly measurable.
2 liters of acid (assuming 31%) seems like more than should be needed on a daily basis.

What kind of test kit are you using?

 

[Caesar]

Thanks Jason, I will start to raising the TA first and see how we go.
I'm using the GUARDEX 4 in 1 PLUS TEST KIT-DPD SWIMMING POOL & SPA TEST KIT.

Yes, we are a hotel.

Cheers
Caesar

 

[jblizzle]

Really having adequate chlorine based on your CYA level is more important that trying to dial in the TA and pH from a safety standpoint. If the FC is not adequate, really the pool should not even be open to your guests.