How Much Chemical Should Be Added At A Time?

[sjt2900]

Our CH has been running about 450-500. We just refilled the tub with soft water and want to raise the CH with Calcium Chloride, 77%. According to The Taylor 2006, the CH is now 10. The pool calculator says to add 7.7 oz of CC to get the CH to 150. I've read so much not to add all the chemical at once, but haven't seen just how much is ok. So should I add 1 oz. at a time or is more ok?

[quantumchromodynamics]

Generally, you want to add 50 to 75% of the calculated amount and then retest before adding more to make sure that you don't overdo it.

Be careful about adding too much calcium because it can form an insulating scale coating on the heater element and cause the element to overheat. I would not exceed 100 ppm unless there is plaster or grout that you need to protect.

Be sure to dissolve the calcium chloride in water in a clean plastic bucket before adding it to the hot tub. Never add more than 4 to 6 ounces per gallon of water because when the calcium dissolves it generates heat.

I would also advise that you use a higher purity than the 77% calcium chloride. Look for something that has in excess of 90% calcium chloride.

[sjt2900]

Whoops! Sorry! The CC is 100%. So I shouldn't go higher than 100 on the CH? The book from Taylor 2006 says 150 to 250 which is what I was going by. I'm still on a learning curve here and don't want to do anything to damage the tub. Also I'll disolve the next couple of oz in water before I add it. But what about the other chemicals to be added for chlorine and ph and such? How much of those should be added at at time?

[quantumchromodynamics]

If

pH = 7.5

Alkalinity = 100 ppm

Calcium = 150 ppm

Temperature = 104 F

then your water is almost perfectly balanced based on the Saturation Index. If your hot tub is plaster, has grout or other such material that requires a near 0 saturation index, then that's fine.

Some tub manufacturers recommend specific calcium levels for longevity of the tub surfaces and elements. You should follow their recommendations.

However, the water in the heater is substantially hotter than the general ambient water temperature. This can lead to scaling of the heater element, and that can cause premature failure because the scale acts like an insulator trapping the heat and overheating the element.

I like to provide a little bit of a negative index to protect the heater from scaling.

Remember the rule that calcium needs to lose heat to dissolve and gain heat to precipitate. The heater provides the heat that causes the calcium carbonate to precipitate and form scale.

I think that going with a 100 ppm calcium is the best level. I don't think that going up to 150 will give you any better performance or results.

[Nitro]

If you're using only Dichlor (granulated chlorine) or Bromine, then a TA of 100ppm and CH of 100ppm is fine. However, if you use Dichlor/Bleach, like I do, you'll need to keep your TA much lower, 50-60ppm. In this case, you'll want to raise your CH to at least 150ppm. Otherwise your SI will be quite low.

[quantumchromodynamics]

Nitro, what would the purpose of a neutral SI be for a tub that does not contain plaster or grout? Is there a significant detriment or risk to materials like fiberglass?

[Nitro]

Nitro, what would the purpose of a neutral SI be for a tub that does not contain plaster or grout? Is there a significant detriment or risk to materials like fiberglass?

I'd say slightly negative SI is good (around -0.35). However, with TA around 50, CH at 100, CYA at 30, Borates at 50 and Salt over 1000 ppm, you'll have a SI of around -0.75 (water temp 100 deg). IMO, that's a little low. Not to mention, as Salt increases the SI will drop further. Also, if people are using Dichlor only (not recommended), SI will lower from CYA.

The jury is still out on whether very low SI will harm the tub and/or plumbing, but I'm not taking the chance. I do agree scaling is also a problem that should be avoided. Balance is the key.

[sjt2900]

With Taylor 2006 the PH is deep pink. 7 drops of acid demand brings it to about 7.6. Is there a way to figure what the PH was by how many drops used?

[PaulR]

The jury is still out on whether very low SI will harm the tub and/or plumbing, but I'm not taking the chance. I do agree scaling is also a problem that should be avoided. Balance is the key.

I've heard that the gelcoat (?) on fiberglass can suffer if SI is very low, like -0.6 or under.

--paulr