I've had my hot tub for 20 years and knew nothing when I first started..Read these easy instructions below..It might help clarify some things for you instead of being overwhelmed...Buy yourself a Taylor K-2006 water testing kit and don't use the strips as they aren't accurate enough and if necessary start with a fresh fill of water..
Water Balance
Water can be either Acidic, Balanced or Alkaline. If your water is not balanced, it could cause all kinds of problems. If it's too Acidic it could cause corrosion. If it's too Alkaline it could cause scaling. Both of which will reduce the effectiveness of your sanitizer. If your water is not balanced then your water is not safe for you, or your tub. So it's really critical to get this correct.
There are four main parameters to keeping your water balanced. Water Temperature, Calcium Hardness (CH), Total Alkalinity (TA) and Potens Hydrogen (pH). Assuming your water temp is around 100 degrees, we'll just focus on CH, TA and pH. The best way to test these is with a Drop Test kit, like the ones mentioned above. IMO Test Strips are just not accurate enough to test these, especially for a beginner.
PH: pH is the measure of acidity in your water. It's on a scale of 0 to 14, 7 being neutral. The human eye has a pH of 7.5, so the ideal range in Pools/Spas is 7.4-7.6 with a min of 7.2 and max of 7.8. However, and this is important, just because you have a pH of 7.5, doesn't mean your water is balanced. If your TA and/or Ch is too high, you could be forming scale in your tub. So it is very important to have balanced water along with an ideal pH.
Total Alkalinity: Alkalinity is a pH Buffer. High levels of TA will not allow pH to change from additions of acid or base. However, a high TA requires a low pH to have balanced water. On the other hand, very low levels of TA will allow the pH to change with very little acid. A very low TA level could cause your pH to drop to low levels, very fast with little acid. Also, the lower your TA, the higher your pH needs to be to have balanced water. So, as you can see, a very low TA can become very unstable.
However, pH will have a tendency to rise with aeration (i.e. use of jets and air), more so if your TA is high. Although, as long as you're not adding Acid (or anything with a lower pH) to your tub, the pH will not usually drop. Therefore, in hot tubs the problem is normally pH rise (or Drift), because of all the aeration. So, the trick is to get the TA high enough to not create an unstable situation, and low enough to not allow pH to rise too much.
Let me repeat the last sentence, because it's the single most important thing to keeping your water balanced. The key to having balanced water, without pH drift, is having the correct TA level. If you find your pH rises too high (>8.0) after using your tub, your TA is too high, and needs to be lowered. If you find your pH is too low and/or your water is continually acidic, your TA is too low and needs to be raised. By fine tuning your TA, you can get your pH perfectly balanced, that rarely needs adjustment.
SO, what's a good TA then? Because spas tend to have a lot of aeration from jets and because the water is hot, it is best to keep the TA low at around 50 ppm.
OK, how do we adjust TA then? If TA is too low, you just add Baking Soda to raise it. However, if TA is high, it's little more involved. You'll need Acid (Dry or Muriatic). Depending on how high your TA is will depend on how long it will take you. Plan on it taking around an hour to decrease TA by 100 ppm. So if your TA is 300 ppm, plan it taking around 2-3 hours. First, uncover your tub and turn on all your jets, air, blowers, waterfalls etc. Test your pH. When it's greater than 7.8, add enough acid to bring it down to 7.0. Keep aerating until your pH is 7.8 again (about 30 min), then add more acid and repeat. Every time you add acid you're lowering your pH and TA. When you get your TA tuned perfectly, your pH will rise to a level (i.e. ~7.6) and stop, then you know you're at your ideal TA level. If your pH is rising too high (>8.0), bring your TA down a little more. If your pH doesn't rise enough from aeration (after an hour or more), you over shot it and need to add a little Baking Soda to raise your TA. After a few days/weeks of monitoring it, you'll get your TA tuned perfectly. You may need to add a little Dry Acid once a week or two, but your water should be well balanced at that point.
I wouldn't go much below 50 ppm TA, because that could become unstable if you add any kind of acid. Also, if you have a high TA, above 100, you may need to add more acid in the beginning to get your pH down. Remember, TA is a pH buffer, so the higher the TA, the more acid you need to bring the pH down. It takes approximately 8 oz total of Dry Acid to bring TA down 100 ppm in a 350 Gal tub. However, the key is not to add too much acid all at once to bring your pH down under 7.0. That's why you should aerate in between adding acid.
