Can't get alkalanity and ph in proper range at the same time

[OkieDust]

I have a Catalina Swim Spa 675gallons.  This mornings test:  Hardness 210ppm, ph 7.5, TA 70ppm.  I use dichlor for my sanitizer.
Using muriatic acid to lower ph and sodium bicarbonate to raise alkalinity.  If I add enough sod bicarb to get alkalinity above 80ppm my ph goes to 7.8.  Then I add enough muriatic acid to get the ph back down to 7.5 and the alkalinity drops to 70.  How can I get the ph in the 7.2-7.5 and alkalinity in the 80-120ppm at the same time?

[wmccall]

Welcome to the forum!   This is far from my expertise, but if my PH is anywhere from 7.2 to 7.8 I don't worry about it.  In your case I'd live with a PH of aroudn 7.6 and let the Alk fall where it may.  (I have never used a swim spa so I don't know if that makes a difference. I don't put my eye in my water.   

[BullFrogSpasMN]

7.5 is perfect and a TA of 70 is a good range as well, why would you adjust it?

[OkieDust]

If TA and ph stayed in that range I'd be a happy camper but the alkalinity drifts and ph drift on a daily basis.  I refilled the spa about three weeks ago.  On that day water was TH 120, TA 105, ph 7.2. I added hardness increaser to 210.  Water crystal clear and it would hold the chlorine in proper level for several days. I'm the only one using the spa and it's for 30 minutes a day. It stayed in that excellent range for about a week but then started to drift.  Alkalinity
yesterday was 70 and today 65. ph 7.5.  Water is not crystal clear anymore and dichlor not holding well.  I put in 1.75oz (3 Tbsp) dichlor yester day and today all ready down to 0.5-1ppm.  Maybe I'm expecting too much but dichor usage seems high and I would like crystal clear water.  I do clean the filters every couple weeks and the filters are about three months old.