New Hot Tubs BUT no or very low Alk

[Nicolavalley]

Hi there, my problem is alkalinity or the lack of it. I have new tubes, new plumbing, new filters pretty much everything is new. The boilers are all that is left from our old tubes.At start up i filled tubes and began to balance the water. My fill water was tested and alkalinity was 90 ppm. BUT by the time the tube is full, i test the water with nothing in it just to see where my water is when i start. CL2 was .2 ppm, ph was 6.8 low anyway and was almost 0. Alk test was like blue, really didnt know if i was hi or low just that there was a problem. Did some homework to find out it was almost 0. So ok i treat alk, and sure almost everything eles fell into place, The next morning alk was at 0 again and chemistry was all over the place. Now im two weeks into this thinking there something prob from construction that is killing my Alk, Dumped water couple times, backwashed and drained filters, completly drained both systems trying to get out whatever it is. Now getting worse have to add sodium bicarbinate twice a day just to keep alk close.It dropped 60-70 ppm by 2pm, like7-8 hours. Help me please, Guess what i really need to know is what kills or neutralizes alk other than acid.....

[chem geek]

Only acid addition, including net acidity from chlorine sources such as Trichlor and Dichlor (since chlorine usage/consumption is acidic) and calcium carbonate precipitation lower Total Alkalinity (TA). Are you sure you don't have an acid feeder that has run amok, possibly due to a pH sensor gone bad?

Or is it possible that your test kit has a problem? Realize that if the disinfectant level is very high, then the TA test will go from blue to yellow instead of from red to green. Blue does NOT mean the TA is zero (where did you read that?). It means that the chlorine level is high, but the TA test can still be done either by adding more of the chlorine neutralizer to it or by titrating to go to yellow.

See this link that says for the TA test:

High halogen level may change indicator reaction from green/red to blue/yellow; to prevent, add thiosulfate prior to testing.

[Nicolavalley]

Ya im thinking hi cl2 over 25ppm sounds about right cause our HRR probe was very slow in responseding when reading cl2 levels, overloaded had to dump more than once.Since than we have replaced that hrr and ph probe.solved one prob just relized there was more than one problem here We had prob after prob with start up, one thing to the next, been huge learning curve and not over yet. Last night at 530pm i tested alk got 120ppm in small Hot Tub and 80ppm in Large tub at closing time.At 530am before opening with no bathers at all. both tubes at 30ppm overnight.I can treat it make it work but just bit worried about adding bicarb twice a day mininal just to maintain levels. I sat watched my controlers see what and when they would start doing funny things. seems as soon as alk gets low like under 30ppm the hrr starts to climb and seen ph go up and down. bottem line keep alk up all balances out but it challenge almost gotta sit and baby it day.