ocean water pools ph and alkalinity

[pelekakias]

Hello there. First of all excuse my bad English .
I found this forum from google after I had some problems with pools so I am happy to post here.
To introduce my self . Iam a pool guy working in a 5star hotel in Greece which has 38 pools .a huge one and small privates ones, I have managed to keep them crystal clear without algae or anything but still have a lot to learn and discover more in pool maintenance.
The water that is used to the most of the pools is water from the ocean . I have a huge pump sucking water from the ocean and fill most of the them(only 2 pools uses sweet water from a river). All the pools luckily are overflow and not skimmer and all of them have sand filters. I have also to mention and I think is quite important that some of the pools loses a lot of water from broken pipes or cracks from bad construction so I need to fill water all the time. I have managed to fix a lot of leaks when hotel is closed in the winter but I have still a few pools with big loss which I believe to fix them all when season ends.
We use liquid chlorine in the big one mostly and trichlor tablets and granules to all the other ones.
Ph minus(muriatic acid) for ph down
soda ash for ph up.
Source water ph with potentiometric(electrode) method
sea : 8,0
river 7,6
source water ph with lovibond phenol red reagents (same to photometer)
sea: 8,2
river 7,6
CYA on pools that lose a lot of water is very low of course. on the other pools is about 60-90 and I have started since one week vacuuming in waste to refill water.

firstly I want to ask an accurate way to test PH in sea water pools after having some huge differences between test methods .. I use dpd1 rapid tablets from lovibond to test the chlorine levels and also phenol red tablets from lovibond for ph levels in a small hand test kit(they are the same for digital photometers, just dissolving faster) . I have also used a Hanna digital potentiometric with glass electrode calibrated very often and mostly the differences between electrode and phenol red tablets are more than 0,4 in the ph scale . Tablets shows 7,6 electrode shows 7,2. always the electrode shows from 0,2 even to 0,6 lower compared to phenol red on seawater pools.
I have also 2 pools that uses sweet water from a river . In that pools is the exact opposite .. electrode shoes 0,2-0,4 more ph than the phenol red and there are only sometimes that they show the same result and only in river water . From my experience I believe the electrode has right at least in sweet water but I am not so sure how all methods behave in such a salty water. I would appreciate if anyone can help me with this .

Second . For 3-4 months in a row ph was always going up a little bit and only in the beginning of the season I had to add muriatic acid to low it at 7,4. then I used trichlor tablets which are very acidic and they lowered the ph even lower but after 1-2 days ph was going back to 7,4-7,6. then tablets again back to 7,2 and then back to 7,6-7,8. I was very happy with that cuz everything seemed normal. But the last month ph always going down and down and I have to add soda ash that lasts only about one week and ph down again to 7,0-7,2 and even lower . I have been terrified because you have to know that in ocean water pools if ph goes lower than 6.8 if it has chlorine in it the water turns in a crystal clear green water. I never understood why that's happening but I have seen it with my eyes a lot of times in the past. A crystal green water , at least its crystal . of course this is not happening in the pools with high loss of water . There the ph goes really high because source water as I mentioned is 8,1. and I just add muriatic acid very often.
I believe something is happening with alkalinity thats why my ph goes down from day to day , but I don’t have tests for alkalinity. And I don’t know what would be an accurate method if it is too sensitive to get fault readings like the ph is . Someone told me the ph goes down because cya is high but I don’t think that's the case . Cuz I have low ph on pools that I have low cya too about 45. and I don’t believe that total cya keeps lowering the ph , it does every time you add tablets a little bit and that's all. Am I right to that?
And finally in the pools with river water keeps makes me so confused. The one that doesn’t lose water at all ph is pretty stable at 7,5. the first 2 months only needed a lit bit of ph minus . The second one with river water again loses a little water so I fill up but not a big amount day per day and that pools ph always going up to 8,2 from 7,2 only in 2 or 3 days .. I have always to add huge amounts of muriatic acid and ph keeps going extreme high despite the fact I use trichlor tablets there too. And the strange thing with this is that this pool source river water ph is 7,6. so how the ph goes so high? Even if I refiled lot of water it shouldn’t go above 7,6.
its strange too that in seawater pools which ph goes really low when I waste and refill a lot of water ph is still low despite the fact that its source water is 8,1. theoretically sea water should get the ph high and river water should get ph down . But its not .
So lets assume that in a seawater pool of 100 tons of water I lose 5 tons of water the day and I refill with high ph water but it makes not a big deal on ph.. it still gets lowering day to day
but in the river one 100tons again losing 5 tons per day again and the ph from 7,4 goes to 8,0 or even to 8,2.
what could be happening ?
Sorry for the huge text and for your hard time to read it . I know my english sucks

[Teapot1]

I would think your biggest issue since you cannot measure it is Alkalinity. That effects pH rising and falling (in the case of acidic chlorine tablets) if you have lovibond brand available then you should be able to get hold of a test kit. Clear green water at low pH is often down to metals in the supply water, often magnesium and copper.
Now get back to work plugging those leaks or youll never get to the end of your issues hahaha.

[pelekakias]

I would think your biggest issue since you cannot measure it is Alkalinity. That effects pH rising and falling (in the case of acidic chlorine tablets) if you have lovibond brand available then you should be able to get hold of a test kit. Clear green water at low pH is often down to metals in the supply water, often magnesium and copper.
Now get back to work plugging those leaks or youll never get to the end of your issues hahaha.

thank you for your answer. 3 days before a chemistry guy who works in a company who sell us the chemicals came to take sample from the rivel pool that i have the problem. he measured ph at 7.9 i measured the same (electrode) . we tried photometric method too and it showed 7.4 . he also tested alkalinity and it was 200. he told me everythig is ok u just need to add acid very often , but for me thas a little bit strange.. ph shouldnt just rising so easy all the time . i made a test that day . i added double the amount of acid just to be sure the alkalinity will go lower than usual . next day i measured and ph was at 6.5. i left it there without doind anything. and next day test again and ph was at 7.3. what the hell is goin on? ok of course the pool was reffiling with fresh water these both days but just only a little amount . i tested cya and its not more than 20ppm. is there any case if i add more cya to get the ph stabilized? and why im thinking that? because the other river pool i mentioned which does not have leaks using the same water has been stabilized at 7.6 for the last 2 months and that pool had cya about 80-90. so i wasted 1/3 of the pools water refilled to get cya lower and still the ph didnt go up..stayed there again. thats really strange cuz they use the same source of water.

[Teapot1]

CYA is a chlorine stabiliser not a pH stabiliser.
With Alk at 200 your pH will constantly rise through off gassing of CO2. If you add acid it lowers both pH and Alk but you then aerate the water to rase the pH and that will Not raise your Alk then you repeat this process often until the pH doesnt drift up with the Alk around 60ppm. All very pointless with your leaks and constant topping up.

[Arthurbub]

is there some kind of formula with mixing a certain amount of RO water set at a certain ph with mixing tap water set at a certain ph, it seems like adding tap water affects the water more so than the RO affecting the water

ive been using API liquid ph test kit, should i get another kind??

[Teapot1]

I would expect tap water to effect things much more because it contains much more it the way of minerals etc that have an over reaching effect. RO water has been stripped of most things so effects would be minimal.