Water Balance Problem

[Freelancer]

I have just filled a 100,000 litre pool with fresh water.

Readings are.
FC 0.0
PH 8.15
Calc 85
CYA 0
Alk 40

So I figure first thing is to get the PH down so I put 10 litres of 20% 13% Bau Acid. 5Kg of CYA and 5 Litres of Chlorine (15%)

New Readings
FC 6.5
PH 7.9
Calc 85
CYA 40
Alk 25

Now I realise that I now have to get the Alk and Calcium up and the PH down a bit further. Only problem is if I put Sodium Bicarbonate in the quantities needed (8Kg)to get the ALK up to 70PPM the PH is going to rise above 8.0 again and if I use Acid to get the PH down then the Alk will just drop.

Normally a new fill has Alk 140 and PH 7.9 so usually a pretty easy fix but for some reason this water is not the norm.

My question is, is it possible to get my Alk up and my PH down using liquid acid (20% 13% Bau) and sodium Bicarbonate? If I was to put 8kg of Sodium Bicarbonate and few litres of 20% acid would one cancel out the other.. I've used the pool calculator but it states that the PH would only rise by 0.1 for 8Kg of Sodium Bicarbonate but I'm not sure as this seems like a very small rise for such a large quantity. Any ideas or thoughts would be appreciated.

 

[Bama Rambler]

Believe what the Pool Calc says. Using Sodium Bicarb raises TA but not pH very much. It's common practice here to do just what you're saying.

 

[duraleigh]

Reinforcing bama's post...

Raise pH - 20 mule team borax....little affect on TA

Lower pH - Muriatic acid - also lowers TA

Raise TA - Baking Soda - little affect on pH

Lower TA - aeration and acid - See Pool School

 

[Freelancer]

Excellent, thanks guys I'll go ahead and post my figures in a week as I find Alk can take a while to show it's true readings.

 

[Freelancer]

Ok here are my reading just before dosing.

100,000 litres

PH 7.9
Alk 35


I put in 8Kg of Sodium Bicarbonate and 10 litres of 20% Acid.

My readings today were
PH 8.0
Alk 50

Great to see the Alk rising by the expected amount but not sure why the PH went up so much given the amount of acid I put.. Guess I'll have to add another 10 litres of acid and slightly less Sodium Bicarb.