When To Add Calcium?

[simonc]

When should I add calcium to balance my water?

More specifically, how long after I add a metal inhibitor should I add calcium? Also, more generally, is there an order to adding chemicals on a new refill? I am using the diclor-then-bleach method which I have found works well for me.

I'm going to do a refill on my fiberglass tub (Jacuzzi brand). Usually, I add a metal inhibitor first thing. Then I add the other chemicals. Prior to joining this forum I never added Calcium (CH). Now this will be my first refill since joining the forum and I plan on adding CH to better balance my water, ala Nitro's recommendations

My tap water CH is low (<100), however I live in a hard water area. I'm on a municipal water supply, but it gets it's water from wells. My water district analysis says that my water hardness (as CaCO3) averages 186ppm with a range of 92-260. I have no idea what that means. All I know is the water here is a lot harder than other areas that I've lived (which get their water from reservoirs).

My tub is over 4 years old and I don't have any visible staining/scaling problems. I've always added metal inhibitor first thing and never added CH. The adage "don't mess with success" comes to mind.

In another thread on this forum, there is a discussion of the problems of adding CH and metal inhibitor at the same time. I guess this is a no-no. Yes, I know I can use a pre-filter but I don't want to spend another $50-$60 on another tub "accessory" unless it's necessary.

So ... what's the right timing for adding CH to balance my water?

- Simon

[PaulR]

I do pH and TA first, then worry about CH later. As it says in the other thread, you don't want to add calcium in conjunction with anything else.

So, do you know what makes the water hard, if it's not calcium? Just wondering if the metal inhibitor is really necessary.

--paulr

[quantumchromodynamics]

If you don't have any plaster or grout, then calcium is not such a big deal. It can help prevent some foaming and it might, or might not, help prevent metal corrosion.

You should first balance all of your other chemicals and then determine the correct amount of calcium to add to achieve a CSI (Calcite Saturation Index) of about -0.2.

You can use thepoolcalculator to calculate your CSI. Be sure to fill in all of the fields to get an accurate calculation.

I don't like to add calcium within 12 hours of any other chemical, especially pH or alkalinity increaser.

I recommend that you only use calcium that is greater than 90 %, not the 77 % stuff. Calcium should be dissolved in cold or cool (not warm or hot) water before being added to the hot tub. Dissolve a maximum of 4 ounces of calcium chloride per 1 gallon of water. Limit calcium additions to 40 ppm per day.

Metal inhibitor is not always needed. If you don't have metals, such as iron, then you don't need a metal inhibitor.

Most likely, the tap water is being reported as "Total Hardness", which includes calcium, magnesium and other minerals.

[simonc]

PaulR & QCD -

Thank you for the help.

I suspect that many spa owners have the same experience as I did ...

Buy a spa, get a bunch of chemicals from the dealer, and then just do what the dealer says without understanding what one is really doing.

I always added the metal inhibitor because that's what the dealer told me to do. I know I have hard water because our municipal source are deep wells. If I pull out the strainer screen on a faucet, rocks (tiny ones) fall out! So far I haven't had any staining or scaling on my fiberglass tub, so I'll probably continue adding the metal inhibitor just because it seems to have "work", i.e., nothing bad happened.

After joining this forum, thanks to people like yourself, I started to understand a little more about why and when to add chemicals. Calcium is still a little bit of a mystery to me. For fiberglass tubs I know it's not that important relative to the issue of staining or scaling. However, I thought it was an important element (no pun intended) in water balancing. To me "water balancing" means maintaining water chemicals so as to maximize sanitation, safety, and comfort, but minimize wear and tear on the tub components (pipes, heaters, pumps, etc.).

In Nitro's writeup on water balancing, he lists calcium as a key component. He says: "Calcium, Baking Soda, Dry Acid and Borates is all you need to balance your water." So ... I figured Calcium is important.

Lastly, what type of Calcium should I use? The pool calculator lists two types: calcium chloride and calcium chloride dihydrate. I think I have the latter, but I'm not sure. (I went to Leslie Pool supply to buy Calcium. They only sell it in a large bucket that would probably last me a few lifetimes. So ... my brother has a pool and I got some from his bucket. However, the bucket didn't say what kind of calcium. I used the directions on the bucket regarding how much to use in a pool to infer that I had calcium chloride dihydrate, but I'm not sure.)

QCD recommends using the 90% calcium. Which kind is that and how do I get it in a reasonable quantity for a hot tub?

- Simon

[chem geek]

A CH level of around 120 ppm or so usually inhibits foaming so that is one reason to have some calcium in the water. In any pool or spa with a plaster/gunite/grout surface exposed to the water, then having the saturation index close to zero is important to protect such surfaces. For fiberglass, it's not as obvious because some fiberglass uses calcium carbonate in the gelcoat while some does not and it's not clear if the water gets exposed to the gelcoat (backing) anyway. To be safe, we usually recommend to have the water somewhat near saturation. As for preventing metal corrosion or for ceramics in pumps, that's more controversial so it's just easier to recommend near-saturation in general as it doesn't hurt unless one doesn't monitor the pH -- that is, if the pH rises too much and you were near saturation, then you could get scaling.

Most calcium chloride is the dihydrate form, but I've purchased anhydrous as well. Basically, if the ingredients list says "calcium chloride" at a concentration of 72-75%, then that's likely to be the dihydrate form that might equivalently say something like "calcium chloride dihydrate" at 96%. This is not bad, but just note that you are paying for water so scale the price up if you are comparing products against anhydrous which says "calcium chloride" usually at 90%. For pools, you can buy larger quantities of Peladow which is 90% Calcium Chloride (anhydrous) or Dowflake which is 96% Calcium Chloride Dihydrate (equivalent to 72% Calcium Chloride Anhydrous).

These raw chemical products probably don't come in small sizes for a hot tub so getting a SpaGuard Calcium Hardness Increaser would be OK -- unfortunately, from the MSDS it's hard to tell it's concentration, but it looks like it might be the anhydrous form assuming the "75-97" range is more like 90. Leisure Time Calcium Booster doesn't say the percentage in its MSDS, but the dosing instructions imply an impure dihydrate form. GLB Calcium Hardness Up normally sold for pools appears to be anhydrous from the dosing though the MSDS is not helpful. The thing is that to raise the CH by 100 ppm in 350 gallons, you only need about 5 ounces weight of calcium chloride anyhdrous while the smallest sizes for the pool products come as 6 pounds compared to 1 quart (maybe 1-1/2 pounds) in spa products. Then again, the spa products are more expensive per pound.

Richard

[simonc]

Richard -

Thanks for the detailed answer. I understand the situation much better now.

Given what you say, I think I have the calcium chloride dihydrate form. Since this is the type I already have, it was "free" (from my brother's pool chemical shed), and it seems to be adequate for hot tub purposes, I'll use it to get my CH level to about 120ppm.

My plan is to ...

1. Refill the tub and add a metal inhibitor because ... well ... this is what I've always done and it seems to work.

2. Balance my water, except for the calcium.

3. Wait a few days and add the calcium as per QCD suggestion that I dissolve it in water before adding it to my tub.

I assume that adding calcium chloride dihydrate (to raise CH from 80 to 120) doesn't significantly effect other pool parameters, i.e., I won't have to rebalance again because of adding the calcium.

- Simon

[quantumchromodynamics]

Calcium chloride is available in two forms.

Regular flake calcium chloride dihydrate (ASTM D 98 Type 1) contains a minimum of 77 % Calcium chloride. It is sold as Dowflake 77-80 % calcium chloride. It is used for applications such as deicing roadways, accelerating concrete set times and for increasing calcium hardness in swimming pools.

The anhydrous form (ASTM D 98 Type 2) is a pelletized calcium chloride with a concentration of at least 94%. This is what is usually sold at pool and spa stores for use in the pool or spa.

If the calcium chloride is in the form of a flake, then it is probably 77 %. If it is in the form of a small pellet or ball, then it is most likely the 94 %.

[Edit] I think that I was probably wrong about determining the form by the shape of the product.

I think as long as the product specifies that the calcium chloride is suitable for use in pools and spas then it is fine to use. I would avoid any calcium chloride that does not specify that it is suitable for pool and spa use. [End Edit]

Either one can be used.

My personal preference is to use the 94 % anhydrous form. I feel like the type sold at pool stores is going to be of higher quality than the stuff sold for deicing roads, but I am not sure of that.

The addition of the calcium chloride should not affect your other chemistry.

Note: Calcium chloride's solubility is inversely proportional to temperature. That means that it is more soluble in cold water than in hot water.

Calcium chloride gives off heat as it dissolves so you have to limit the amount you dissolve at any one time or the mix could overheat.

[simonc]

Calcium chloride is available in two forms.

Regular flake calcium chloride dihydrate (ASTM D 98 Type 1) contains a minimum of 77 % Calcium chloride. It is sold as Dowflake 77-80 % calcium chloride. It is used for applications such as deicing roadways, accelerating concrete set times and for increasing calcium hardness in swimming pools.

The anhydrous form (ASTM D 98 Type 2) is a pelletized calcium chloride with a concentration of at least 94%. This is what is usually sold at pool and spa stores for use in the pool or spa.

If the calcium chloride is in the form of a flake, then it is probably 77 %. If it is in the form of a small pellet or ball, then it is most likely the 94 %.

Either one can be used.

My personal preference is to use the 94 % anhydrous form. I feel like the type sold at pool stores is going to be of higher quality than the stuff sold for deicing roads, but I am not sure of that.

The addition of the calcium chloride should not affect your other chemistry.

Note: Calcium chloride's solubility is inversely proportional to temperature. That means that it is more soluble in cold water than in hot water.

Calcium chloride gives off heat as it dissolves so you have to limit the amount you dissolve at any one time or the mix could overheat.

QCD -

I have the pellet kind, they look like tiny white balls ... a little smaller than BBs. So ... that's Calcium Chloride, not calcium chloride dihydrate. Correct?

The reason I ask is that the Pool Calculator calculates different quantities depending on the type of Calcium.

The Leslie Pool product Hardness Plus doesn't specify what kind of Calcium it is.

- Simon

[quantumchromodynamics]

Based on the dosing instructions, the Leslie's Hardness Plus is probably calcium chloride dihydrate. I know that it comes in the small ball or pellet form. I think that I was probably wrong about determining the form by the shape of the product.

I think as long as the product specifies that the calcium chloride is suitable for use in pools and spas then it is fine to use. I would avoid any calcium chloride that does not specify that it is suitable for pool and spa use.

[simonc]

Based on the dosing instructions, the Leslie's Hardness Plus is probably calcium chloride dihydrate. I know that it comes in the small ball or pellet form. I think that I was probably wrong about determining the form by the shape of the product.

I think as long as the product specifies that the calcium chloride is suitable for use in pools and spas then it is fine to use. I would avoid any calcium chloride that does not specify that it is suitable for pool and spa use.

QCD -

Thanks for the clarification.

- Simon

[Hey harry]

Is there a precaution you are supposed to follow where you wait a period of time after adding Leisure Time SPA UP, before you add Leisure Time Calcium  Booster?   I think i had heard that calcium booster reacts with  SPA UP (sodium bicarbonate) producing a byproduct that is difficult to clean out of a hot tub and its piping. Am i correct about this?

[dashmer]

It is a good idea to wait at least 30 min and preferably a bit longer between adding chemicals to your water. When I fill, after my metal sequestrant, I add CH before anything else.  I am not familiar with the reaction you describe but it can be avoided by delays between chems.

It is also a good idea to start a new thread when posting a question.  This one is 13 years old.

 

Good luck.