Dosage Question

[matchu36]

Hello everyone I am looking for some advice here. SLAM in the Pool Math app tells me to add 29 oz by weight of my 70% Cal Hypo to achieve the recommended FC level. My concern and confusion is that I have a 50 lb container of the stuff and I believe the dosage cup as other measuring cups are ounces by volume and this wouldn’t necessarily be a 1:1 equivalent unless the stuff actually is 1 oz weight to 1 oz volume.

Anyway if anyone could give me some pointers I’d be grateful. Only my second year with the pool and still learning the do’s and don’t.

 

[DrewLG]

A web search says calcium hypochlorite weighs 2.35 grams/cubic centimeter, which is 2.45 ounces per fluid ounce. So 29 ounces by weight would be around 12 fluid ounces, or a cup and a half.

But two things:

A little kitchen scale will come in handy for lots more than this, and you can get one that's good enough for under $15.

A SLAM with cal-hypo will add a lot of calcium to your pool -- for every 10ppm FC you add, you'll also get 7ppm CH -- and the calcium will not dissipate or evaporate. So be sure to keep an eye on your CH level, and switch to liquid chlorine when necessary.

 

[matchu36]

A web search says calcium hypochlorite weighs 2.35 grams/cubic centimeter, which is 2.45 ounces per fluid ounce. So 29 ounces by weight would be around 12 fluid ounces, or a cup and a half.

But two things:

A little kitchen scale will come in handy for lots more than this, and you can get one that's good enough for under $15.

A SLAM with cal-hypo will add a lot of calcium to your pool -- for every 10ppm FC you add, you'll also get 7ppm CH -- and the calcium will not dissipate or evaporate. So be sure to keep an eye on your CH level, and switch to liquid chlorine when necessary.

Thank you for that. My calcium tested yesterday at 250 so I am not too concerned about it getting out of control. While waiting for my post to be approved I found a nice calculator called Aqua-Calc which looks to come up with the same values as you presented here.

 

[duraleigh]

Welcome to the forum

My calcium tested yesterday at 250 so I am not too concerned about it getting out of control.

I would be just a bit more concerned. CH seems to build up more quickly than folks think and it's a pain to get rid of.

250 CH is enough and keeps you in the 250-400 range as recommended.

 

[Mdragger88]

One other thing about cal hypo. It can cause cloudiness when using large amounts such as during slam which complicates matters since crystal clear water is one of the three end of
SLAM Process exit criteria.
Cal hypo & calcium chloride can also do this when added around the same time as baking soda in some instances as well.
YMMV.
So it’s recommended to stick with liquid chlorine.

 

[matchu36]

Welcome to the forum


I would be just a bit more concerned. CH seems to build up more quickly than folks think and it's a pain to get rid of.

250 CH is enough and keeps you in the 250-400 range as recommended.

Thank you for that. My apologies as I am trying to follow the Pool Math app which suggests 250 as a minimum for CH levels, as do you. Make no mistake I do not know better than the experts here as I’m still trying to figure this out. That said, the pool is still relatively new having been built and completed in 11/2022 and I have added hardness increaser several times and it continues to fall over time. I was told by my pool builder to purchase a 50 lb container of 70% Cal Hypo when completed and that’s what I did. I was unaware of some of the potential side effects at the time like those similar to what you mentioned. However, considering this is what I have on hand and still a bit remaining in the bucket, I can’t simply justify the switch to liquid at this time. I will however take your advice and carefully monitor the CH levels. In southeast Louisiana, I find myself draining my pool level more often than filling due to rainfall amounts.

One other thing about cal hypo. It can cause cloudiness when using large amounts such as during slam which complicates matters since crystal clear water is one of the three end of
SLAM Process exit criteria.
Cal hypo & calcium chloride can also do this when added around the same time as baking soda in some instances as well.
YMMV.
So it’s recommended to stick with liquid chlorine.

My pool is crystal clear but I’m battling stubborn yellow algae in spots along the walls and steps. I was mislead by my PB to think the UV system was the workhorse of my sanitizing system and I failed at monitoring my fc levels for a period of time. Then my UV lights went out. And now trying to SLAM but realized earlier per my initial post that I have been following the pool math app incorrectly because the dosages for CalHypo are in weights and not by volume and I have always been adding the suggested amounts as a volume like a big dummy . I do thank everyone for their input. I will make sure to get my hands on some liquid chlorine as suggested I was just trying to use what I have already on hand.