Chemical inbalance but which do I adjust first?

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rehab
Pool Newbie
Pool Newbie
Posts: 4
Joined: Tue 01 Dec, 2009 02:37
My Pool: Pool size 8.5m long x 4.5m wide x 1.5m Avg depth
Concrete, pebble crete
Pump 1.5HP Monarch Silensor
Sand Filter 28" Monarch
Chlorinator 24g/hr Aquasphere
Location: Australia

Chemical inbalance but which do I adjust first?

Postby rehab » Tue 01 Dec, 2009 04:19

Hi,
I have a new (2 weeks old) salt water concrete pool about 60,000lts.
Latest Pool shop tests of the water are as follows
Salt 5500
Sunscreen 35
Free chlorine 0.22
TDS 5500
pH 8.6
Alkalinity 75
Calcium 60
Water temp about 30c

I understand the pH is high, Chlorine is low, alkalinity is low and calcium is low but which chemical do I try to adjust first?
Do I try and lower the pH before I try and raise the chlorine?
Do I raise the Alkalinity before the above?

I have added about 4lts of pH decreaser and added chlorine but the tests done show very little change to pH or chlorine.
I am running the pump/chlorinator 8 hours a day and the pool has low usage.

Any help would be much appreciated


Guest

Chemical inbalance but which do I adjust first?

Postby Guest » Tue 01 Dec, 2009 05:56

Hi rehab

Your chlorine (FC) is low and the calcium hardness (CH) is low. Low hardness will cause etching of concrete pools, especially when they are new. This can be addressed by adding calcium hypochlorite (perhaps a shock) which will increase the FC and the CH.

Then add pH decreaser to get the pH down to 7.6

Once you have done this test again and post your results here.
Guest

Chemical inbalance but which do I adjust first?

Postby Guest » Wed 02 Dec, 2009 05:02

Ditto. Add cal hypo as a shock and reduce ph first.
czechmate
Swimming Pool Superstar
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Posts: 401
Joined: Sat 16 May, 2009 09:20
My Pool: 16 x 32 gunite21000 gal., Diamond Brite Blue, Swimquip XL pump, DE36
Location: Texas

Chemical inbalance but which do I adjust first?

Postby czechmate » Wed 02 Dec, 2009 09:06

Rule of thumb is to do the PH first. And do not bother to drive to pool store to spend the extra money for a PH DECREASER. Buy a plain baking soda for 50cents a pound in Walmart! Chlorine will not work fully until your PH is in the proper range. TA will change a little with the soda addition. Than you will have more correct decision. Algae is not a much of a threat in cold water. Scaling or leaching is.
chem geek
Pool Industry Leader
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Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Chemical inbalance but which do I adjust first?

Postby chem geek » Wed 02 Dec, 2009 10:07

Read Water Balance for SWGs and note that you don't want the TA to be very high and probably want to keep it around 70 or 80 ppm. This will help reduce the rate of pH rise. You can also use 50 ppm Borates as well.

You would normally use Muriatic Acid from a hardware / big-box store to lower the pH and should do that first. Baking Soda from the grocery / big-box store would be used to raise the TA (with little change in pH), but as I said above, you probably do not need to raise the TA or at least not very much. A higher TA will result in a faster pH rise over time because TA is not only a pH buffer but also a SOURCE of rising pH itself (from carbon dioxide outgassing).

Use The Pool Calculator to calculate dosages and note that you will need to increase the Calcium Hardness (CH) level to protect your concrete pool -- you'll want the saturation index to be closer to zero, though can be slightly negative (not lower than -0.2 -- target either that or -0.1 as the SWG tends to climb in pH and also tends to scale in the cell -- the Borates will help prevent that). You'll probably need a higher than normal CH if you have a lower TA. Check with your builder for when to increase CH since your concrete is new and curing (so CH will rise from that, as will pH).

"Sunscreen" is called Cyanuric Acid (CYA) and should be higher if your pool is exposed to direct sunlight. Note that your Free Chlorine (FC) should be around 5% of the CYA level so if you raise the CYA to 80 ppm if your pool gets a lot of sunlight all day, then you'd need to set a minimum FC target of 4 ppm. You should find that having the higher CYA (assuming direct sunlight) lowers the chlorine demand and that lets you turn down your SWG on-time which will reduce the rate of pH rise as well (less aeration for less carbon dioxide outgassing and less undissolved chlorine outgassing). The use of 50 ppm Borates will not only act as a pH buffer, but may lower chlorine demand due to its algaecidal properties. HOWEVER, note that a new concrete (or plaster) pool tends to rise in pH a lot in the first months due to curing. There's nothing you can do about that and will just need to add a lot of acid regularly, but over time this will decrease.

By the way, your 30C water temp is equivalent to 86F so is not cold.
rehab
Pool Newbie
Pool Newbie
Posts: 4
Joined: Tue 01 Dec, 2009 02:37
My Pool: Pool size 8.5m long x 4.5m wide x 1.5m Avg depth
Concrete, pebble crete
Pump 1.5HP Monarch Silensor
Sand Filter 28" Monarch
Chlorinator 24g/hr Aquasphere
Location: Australia

Chemical inbalance but which do I adjust first?

Postby rehab » Wed 02 Dec, 2009 16:51

Hi Guy's,
Thanks heaps for all your help. I did what you said and added pH reducer and also added stabilised chlorine over the last couple of days.
My test kit this morning shows I am about 1.0 of CL (Moved up from 0)
I hit it hard with the pH reducer (I gave it about a Ltr) and the pH is now about 7.4 (Moved down from about 8.6)
So I think I am within the ball park. I will keep testing but at least I have an idea of what to do now.
I will get a pool shop test done to tell me all the other readings.

Thanks again for your help.......I am sure I will be back with some more problems/questions in the coming weeks. In the mean time I will keep reading the FAQ and try to get a better understanding of pool chemistry.

Rehab :thumbup:
Guest

Chemical inbalance but which do I adjust first?

Postby Guest » Wed 02 Dec, 2009 17:41

And get yourself a decent test kit rather than having to rely on the pool store, who will always want to sell you as much chemicals as possible :wink:
rehab
Pool Newbie
Pool Newbie
Posts: 4
Joined: Tue 01 Dec, 2009 02:37
My Pool: Pool size 8.5m long x 4.5m wide x 1.5m Avg depth
Concrete, pebble crete
Pump 1.5HP Monarch Silensor
Sand Filter 28" Monarch
Chlorinator 24g/hr Aquasphere
Location: Australia

Chemical inbalance but which do I adjust first?

Postby rehab » Wed 02 Dec, 2009 17:59

Hi "Pool User",
Can you tell me the best kit to buy please and or a WEB address of where to get it?
I agree with you re the Pool shops they Suck! I went to three different pool shops with the same sample water and they all came up with different results for example Stabiliser the three readings were, 30, 35 & 70 and all from the same water sample. So yes I would prefer to do all the testing myself and with the forums help work out how much of what I need to add and when.

Cheers Rehab
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Chemical inbalance but which do I adjust first?

Postby chem geek » Thu 03 Dec, 2009 01:46

You can get the Taylor K-2006 for a good online price here or you can get the TF100 from tftestkits.net here . The latter kit ha 36% more volume of reagents so is less expensive per test. The test kits are compared here . You won't go wrong with either one.

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