How Much Muriatic Acid To Lower Alkalinity In A Pool? (Calculator & Chart)

Muriatic acid is a common household name in pool care. Also known as hydrochloric acid, though a diluted and less pure version of it, muriatic acid is a strong acid used for cleaning purposes. It is much cheaper and easy to afford compared to other similar chemicals for pool care.

Along with balancing the pH levels of your pool water, muriatic acid is strong enough to kill mold, remove rust stains, get rid of calcium deposits, and clean the surfaces of your pool.

How much muriatic acid you will need to lower the alkalinity of a pool will depend to some extent on the capacity of the pool.

A pool containing, say, about 15,000 gallons of water, will show a reduction in total alkalinity of about 50 ppm (parts per million) when a gallon of muriatic acid is added.

Muriatic acid pool calculator

We assume that you know the volume of your pool. Also, we assume you have tested your pool and know the current level of its alkalinity.

With that, you would know the amount of alkalinity increase needed to get to the recommended range of 80 ppm – 120 ppm. For example, if the current alkalinity is 160 ppm, that means you need at least 30 ppm and at most 70 ppm decrease to get the alkalinity within the recommended range.

With that in mind, we can continue with the calculation.

To know the amount of muriatic to add to your pool, first, you need to know how much the alkalinity of your pool will decrease by adding 1 gallon of muriatic acid. Below is the simple calculation to do so:

Alkalinity Decrease with 1 gallon (AD₁) = (50 * 15,000) / Pool Volume

Then to determine the amount of muriatic acid required to increase the alkalinity to the recommended range, use the formula below:

Amount of muriatic acid required (gal) = (1 * Required Alkalinity Increase) / AD₁

For example:

Your pool is tested and the alkalinity is 160 ppm and you want to decrease it by 40 ppm so the pool alkalinity will become 120 ppm. Assuming your pool volume is 10,000 gallons, how much muriatic acid do you need?

First, we calculate the alkalinity increase when 1 gallon of muriatic acid is added to the pool.

AD₁ = (50 * 15,000) / 10,000 = 75 ppm

Then you calculate the amount of muriatic acid to add to the pool to give you a 40 ppm decrease.

Amount of muriatic acid required (gal) = (1 * 40) / 75 = 0.53 gallon

So, adding 0.53 gallon of muriatic acid will decrease your 10,000-gallon pool alkalinity by 40 ppm. That amount will take the pool alkalinity to about 120 ppm.

If you are still confused with the calculations, you don’t need to bother yourself. We have already done the calculations for you.

The table below contains the amount of muriatic acid you need to add to your pool to get the required alkalinity increase.

It comprises about 130 different pool volumes. In the first column, you can find a volume that matches your pool. Then the row will help you to find the required amount of muriatic acid for the alkalinity increase.

	Decrease By	Decrease By	Decrease By	Decrease By	Decrease By	Decrease By	Decrease By	Decrease By	Decrease By	Decrease By
Pool Volume (gallon)	5 ppm	10 ppm	15 ppm	20 ppm	25 ppm	30 ppm	35 ppm	40 ppm	45 ppm	50 ppm
2,500	0.02	0.03	0.05	0.07	0.08	0.10	0.12	0.13	0.15	0.17
3,000	0.02	0.04	0.06	0.08	0.10	0.12	0.14	0.16	0.18	0.20
3,200	0.02	0.04	0.06	0.09	0.11	0.13	0.15	0.17	0.19	0.21
3,400	0.02	0.05	0.07	0.09	0.11	0.14	0.16	0.18	0.20	0.23
4,000	0.03	0.05	0.08	0.11	0.13	0.16	0.19	0.21	0.24	0.27
4,600	0.03	0.06	0.09	0.12	0.15	0.18	0.21	0.25	0.28	0.31
5,000	0.03	0.07	0.10	0.13	0.17	0.20	0.23	0.27	0.30	0.33
5,300	0.04	0.07	0.11	0.14	0.18	0.21	0.25	0.28	0.32	0.35
5,700	0.04	0.08	0.11	0.15	0.19	0.23	0.27	0.30	0.34	0.38
5,800	0.04	0.08	0.12	0.15	0.19	0.23	0.27	0.31	0.35	0.39
5,900	0.04	0.08	0.12	0.16	0.20	0.24	0.28	0.31	0.35	0.39
6,400	0.04	0.09	0.13	0.17	0.21	0.26	0.30	0.34	0.38	0.43
6,800	0.05	0.09	0.14	0.18	0.23	0.27	0.32	0.36	0.41	0.45
7,000	0.05	0.09	0.14	0.19	0.23	0.28	0.33	0.37	0.42	0.47
7,500	0.05	0.10	0.15	0.20	0.25	0.30	0.35	0.40	0.45	0.50
7,600	0.05	0.10	0.15	0.20	0.25	0.30	0.35	0.41	0.46	0.51
7,800	0.05	0.10	0.16	0.21	0.26	0.31	0.36	0.42	0.47	0.52
8,000	0.05	0.11	0.16	0.21	0.27	0.32	0.37	0.43	0.48	0.53
8,200	0.05	0.11	0.16	0.22	0.27	0.33	0.38	0.44	0.49	0.55
8,300	0.06	0.11	0.17	0.22	0.28	0.33	0.39	0.44	0.50	0.55
8,400	0.06	0.11	0.17	0.22	0.28	0.34	0.39	0.45	0.50	0.56
8,600	0.06	0.11	0.17	0.23	0.29	0.34	0.40	0.46	0.52	0.57
8,900	0.06	0.12	0.18	0.24	0.30	0.36	0.42	0.47	0.53	0.59
9,000	0.06	0.12	0.18	0.24	0.30	0.36	0.42	0.48	0.54	0.60
9,100	0.06	0.12	0.18	0.24	0.30	0.36	0.42	0.49	0.55	0.61
9,300	0.06	0.12	0.19	0.25	0.31	0.37	0.43	0.50	0.56	0.62
9,600	0.06	0.13	0.19	0.26	0.32	0.38	0.45	0.51	0.58	0.64
9,700	0.06	0.13	0.19	0.26	0.32	0.39	0.45	0.52	0.58	0.65
10,000	0.07	0.13	0.20	0.27	0.33	0.40	0.47	0.53	0.60	0.67
10,200	0.07	0.14	0.20	0.27	0.34	0.41	0.48	0.54	0.61	0.68
10,300	0.07	0.14	0.21	0.27	0.34	0.41	0.48	0.55	0.62	0.69
10,400	0.07	0.14	0.21	0.28	0.35	0.42	0.49	0.55	0.62	0.69
10,500	0.07	0.14	0.21	0.28	0.35	0.42	0.49	0.56	0.63	0.70
10,600	0.07	0.14	0.21	0.28	0.35	0.42	0.49	0.57	0.64	0.71
10,700	0.07	0.14	0.21	0.29	0.36	0.43	0.50	0.57	0.64	0.71
10,800	0.07	0.14	0.22	0.29	0.36	0.43	0.50	0.58	0.65	0.72
11,000	0.07	0.15	0.22	0.29	0.37	0.44	0.51	0.59	0.66	0.73
11,500	0.08	0.15	0.23	0.31	0.38	0.46	0.54	0.61	0.69	0.77
11,800	0.08	0.16	0.24	0.31	0.39	0.47	0.55	0.63	0.71	0.79
11,900	0.08	0.16	0.24	0.32	0.40	0.48	0.56	0.63	0.71	0.79
12,000	0.08	0.16	0.24	0.32	0.40	0.48	0.56	0.64	0.72	0.80
12,200	0.08	0.16	0.24	0.33	0.41	0.49	0.57	0.65	0.73	0.81
12,600	0.08	0.17	0.25	0.34	0.42	0.50	0.59	0.67	0.76	0.84
13,000	0.09	0.17	0.26	0.35	0.43	0.52	0.61	0.69	0.78	0.87
13,200	0.09	0.18	0.26	0.35	0.44	0.53	0.62	0.70	0.79	0.88
13,400	0.09	0.18	0.27	0.36	0.45	0.54	0.63	0.71	0.80	0.89
13,500	0.09	0.18	0.27	0.36	0.45	0.54	0.63	0.72	0.81	0.90
13,600	0.09	0.18	0.27	0.36	0.45	0.54	0.63	0.73	0.82	0.91
14,000	0.09	0.19	0.28	0.37	0.47	0.56	0.65	0.75	0.84	0.93
14,400	0.10	0.19	0.29	0.38	0.48	0.58	0.67	0.77	0.86	0.96
14,500	0.10	0.19	0.29	0.39	0.48	0.58	0.68	0.77	0.87	0.97
14,700	0.10	0.20	0.29	0.39	0.49	0.59	0.69	0.78	0.88	0.98
14,800	0.10	0.20	0.30	0.39	0.49	0.59	0.69	0.79	0.89	0.99
14,900	0.10	0.20	0.30	0.40	0.50	0.60	0.70	0.79	0.89	0.99
15,000	0.10	0.20	0.30	0.40	0.50	0.60	0.70	0.80	0.90	1.00
15,200	0.10	0.20	0.30	0.41	0.51	0.61	0.71	0.81	0.91	1.01
15,300	0.10	0.20	0.31	0.41	0.51	0.61	0.71	0.82	0.92	1.02
15,400	0.10	0.21	0.31	0.41	0.51	0.62	0.72	0.82	0.92	1.03
16,500	0.11	0.22	0.33	0.44	0.55	0.66	0.77	0.88	0.99	1.10
16,900	0.11	0.23	0.34	0.45	0.56	0.68	0.79	0.90	1.01	1.13
17,000	0.11	0.23	0.34	0.45	0.57	0.68	0.79	0.91	1.02	1.13
17,200	0.11	0.23	0.34	0.46	0.57	0.69	0.80	0.92	1.03	1.15
17,300	0.12	0.23	0.35	0.46	0.58	0.69	0.81	0.92	1.04	1.15
17,400	0.12	0.23	0.35	0.46	0.58	0.70	0.81	0.93	1.04	1.16
17,600	0.12	0.23	0.35	0.47	0.59	0.70	0.82	0.94	1.06	1.17
18,000	0.12	0.24	0.36	0.48	0.60	0.72	0.84	0.96	1.08	1.20
18,500	0.12	0.25	0.37	0.49	0.62	0.74	0.86	0.99	1.11	1.23
18,600	0.12	0.25	0.37	0.50	0.62	0.74	0.87	0.99	1.12	1.24
18,900	0.13	0.25	0.38	0.50	0.63	0.76	0.88	1.01	1.13	1.26
19,000	0.13	0.25	0.38	0.51	0.63	0.76	0.89	1.01	1.14	1.27
19,200	0.13	0.26	0.38	0.51	0.64	0.77	0.90	1.02	1.15	1.28
19,400	0.13	0.26	0.39	0.52	0.65	0.78	0.91	1.03	1.16	1.29
19,700	0.13	0.26	0.39	0.53	0.66	0.79	0.92	1.05	1.18	1.31
20,000	0.13	0.27	0.40	0.53	0.67	0.80	0.93	1.07	1.20	1.33
20,100	0.13	0.27	0.40	0.54	0.67	0.80	0.94	1.07	1.21	1.34
20,200	0.13	0.27	0.40	0.54	0.67	0.81	0.94	1.08	1.21	1.35
20,300	0.14	0.27	0.41	0.54	0.68	0.81	0.95	1.08	1.22	1.35
20,400	0.14	0.27	0.41	0.54	0.68	0.82	0.95	1.09	1.22	1.36
20,500	0.14	0.27	0.41	0.55	0.68	0.82	0.96	1.09	1.23	1.37
21,000	0.14	0.28	0.42	0.56	0.70	0.84	0.98	1.12	1.26	1.40
21,200	0.14	0.28	0.42	0.57	0.71	0.85	0.99	1.13	1.27	1.41
21,600	0.14	0.29	0.43	0.58	0.72	0.86	1.01	1.15	1.30	1.44
21,700	0.14	0.29	0.43	0.58	0.72	0.87	1.01	1.16	1.30	1.45
21,900	0.15	0.29	0.44	0.58	0.73	0.88	1.02	1.17	1.31	1.46
22,100	0.15	0.29	0.44	0.59	0.74	0.88	1.03	1.18	1.33	1.47
22,200	0.15	0.30	0.44	0.59	0.74	0.89	1.04	1.18	1.33	1.48
22,800	0.15	0.30	0.46	0.61	0.76	0.91	1.06	1.22	1.37	1.52
23,000	0.15	0.31	0.46	0.61	0.77	0.92	1.07	1.23	1.38	1.53
23,500	0.16	0.31	0.47	0.63	0.78	0.94	1.10	1.25	1.41	1.57
23,600	0.16	0.31	0.47	0.63	0.79	0.94	1.10	1.26	1.42	1.57
24,000	0.16	0.32	0.48	0.64	0.80	0.96	1.12	1.28	1.44	1.60
24,300	0.16	0.32	0.49	0.65	0.81	0.97	1.13	1.30	1.46	1.62
24,400	0.16	0.33	0.49	0.65	0.81	0.98	1.14	1.30	1.46	1.63
25,000	0.17	0.33	0.50	0.67	0.83	1.00	1.17	1.33	1.50	1.67
25,400	0.17	0.34	0.51	0.68	0.85	1.02	1.19	1.35	1.52	1.69
25,700	0.17	0.34	0.51	0.69	0.86	1.03	1.20	1.37	1.54	1.71
25,900	0.17	0.35	0.52	0.69	0.86	1.04	1.21	1.38	1.55	1.73
26,800	0.18	0.36	0.54	0.71	0.89	1.07	1.25	1.43	1.61	1.79
27,000	0.18	0.36	0.54	0.72	0.90	1.08	1.26	1.44	1.62	1.80
27,100	0.18	0.36	0.54	0.72	0.90	1.08	1.26	1.45	1.63	1.81
29,000	0.19	0.39	0.58	0.77	0.97	1.16	1.35	1.55	1.74	1.93
29,200	0.19	0.39	0.58	0.78	0.97	1.17	1.36	1.56	1.75	1.95
29,500	0.20	0.39	0.59	0.79	0.98	1.18	1.38	1.57	1.77	1.97
30,000	0.20	0.40	0.60	0.80	1.00	1.20	1.40	1.60	1.80	2.00
30,200	0.20	0.40	0.60	0.81	1.01	1.21	1.41	1.61	1.81	2.01
30,300	0.20	0.40	0.61	0.81	1.01	1.21	1.41	1.62	1.82	2.02
30,600	0.20	0.41	0.61	0.82	1.02	1.22	1.43	1.63	1.84	2.04
32,400	0.22	0.43	0.65	0.86	1.08	1.30	1.51	1.73	1.94	2.16
32,700	0.22	0.44	0.65	0.87	1.09	1.31	1.53	1.74	1.96	2.18
32,800	0.22	0.44	0.66	0.87	1.09	1.31	1.53	1.75	1.97	2.19
33,000	0.22	0.44	0.66	0.88	1.10	1.32	1.54	1.76	1.98	2.20
33,700	0.22	0.45	0.67	0.90	1.12	1.35	1.57	1.80	2.02	2.25
34,000	0.23	0.45	0.68	0.91	1.13	1.36	1.59	1.81	2.04	2.27
34,300	0.23	0.46	0.69	0.91	1.14	1.37	1.60	1.83	2.06	2.29
34,500	0.23	0.46	0.69	0.92	1.15	1.38	1.61	1.84	2.07	2.30
36,000	0.24	0.48	0.72	0.96	1.20	1.44	1.68	1.92	2.16	2.40
36,300	0.24	0.48	0.73	0.97	1.21	1.45	1.69	1.94	2.18	2.42
37,500	0.25	0.50	0.75	1.00	1.25	1.50	1.75	2.00	2.25	2.50
37,700	0.25	0.50	0.75	1.01	1.26	1.51	1.76	2.01	2.26	2.51
37,900	0.25	0.51	0.76	1.01	1.26	1.52	1.77	2.02	2.27	2.53
38,800	0.26	0.52	0.78	1.03	1.29	1.55	1.81	2.07	2.33	2.59
39,400	0.26	0.53	0.79	1.05	1.31	1.58	1.84	2.10	2.36	2.63
39,600	0.26	0.53	0.79	1.06	1.32	1.58	1.85	2.11	2.38	2.64
41,900	0.28	0.56	0.84	1.12	1.40	1.68	1.96	2.23	2.51	2.79
42,200	0.28	0.56	0.84	1.13	1.41	1.69	1.97	2.25	2.53	2.81
43,100	0.29	0.57	0.86	1.15	1.44	1.72	2.01	2.30	2.59	2.87
45,000	0.30	0.60	0.90	1.20	1.50	1.80	2.10	2.40	2.70	3.00
46,900	0.31	0.63	0.94	1.25	1.56	1.88	2.19	2.50	2.81	3.13
47,900	0.32	0.64	0.96	1.28	1.60	1.92	2.24	2.55	2.87	3.19
50,500	0.34	0.67	1.01	1.35	1.68	2.02	2.36	2.69	3.03	3.37
56,200	0.37	0.75	1.12	1.50	1.87	2.25	2.62	3.00	3.37	3.75
58,900	0.39	0.79	1.18	1.57	1.96	2.36	2.75	3.14	3.53	3.93
67,300	0.45	0.90	1.35	1.79	2.24	2.69	3.14	3.59	4.04	4.49

Does adding diluted muriatic acid at one spot in a pool deep end increase only pH?

If you are pondering upon this question, then you must have stumbled upon the old pool myth concerning the addition of muriatic acid in pool water.

How what part of your pool you add muriatic acid will determine if only pH will be lowered, or both alkalinity and pH will be lowered.

The former is when muriatic acid is added in a spot at the pool’s deep end, and the latter is when it is added around the perimeter.

Adding diluted muriatic acid at one spot in the deep end of your pool does not just increase only pH. what part of the pool you apply the muriatic acid does not have any part to play on the chemical reaction that takes place.

The main issue of concern should rather be how to go about applying muriatic acid in your pool water.

The best explanation for this misconception may be the fact that some chemical reactions take time to take effect. A pool as you know is not exactly a tiny body of water.

So it is going to take some time for the muriatic acid you added to spread across from whatever part of the pool you added it to every other part. If you take your readings a little after adding the chemical, be sure to do something that is not accurate.

This is why it is always advised to take readings after some specific period, depending on what chemical is being added to the pool.

Muriatic acid will lower both pH and alkalinity, despite where it comes in contact with the pool water. And it can take about 24 hours for muriatic to react completely with balanced pool water, meaning you just have to let it spread out first.

How to add muriatic acid to pool water?

Muriatic acid is a very strong acid, capable of corroding virtually everything, plastics, clothes, metals, you name them. This makes it very effective in adjusting water pH in a pool.

But on the downside, your pool coatings and equipment are not acid invincible, and neither is your skin. So when handling muriatic acid, you have to be aware of its high corrosive ability and take necessary precautions to avoid causing harm to yourself and your pool.

If you intend to clean your pool and balance your pool pH by adding muriatic acid, then below is a step-by-step approach on how to add muriatic acid to your pool water.

Step 1: Test for the pH of the pool water. You need to be certain if lowering pool pH is what is needed, and what amount of what is needed you out to add get the desired results.

Step 2: Water protective pieces of equipment. You can never be too careful, and accidents might happen. So proper clothing for your skin, rubber gloves, lung protection, and eye protection goggles can be the deciding factor between a severe burn, a breath of death, and a harmless spill.

Keep baking soda at standby to neutralize any spilled muriatic acid quickly.

Step 3: Dilute the acid. As a very strong acid, pouring muriatic acid in undiluted form into your pool is a bad idea, highly unsafe. When it enters the water in its concentrated form, it is not going to dissolve immediately.

It can take up to 24 hours for muriatic acid to react with pool water. So anything coming in contact with it at that period is going to be corroded, and your pool linings, equipment, and pipings are not left out.

Fill a bucket of water halfway before adding your acid to it to dilute it. It should never be the other way round, but rather a water first before acid. Putting acid first can result in accidental splashing of acid as water is being poured.

There could also be reactions leading to fumes that you risk inhaling. Inhaling muriatic acid fumes can cause issues with lunges and breathing, so avoid direct inhalation.

Dilute according to the instructions on the acid label. Or use an online calculator to know what amount you are working with. 1 part of muriatic acid for every 10 parts of water is ideal to work with.

For the sake of clarity, this should be about 4 cups of acid per half of a 5-gallon bucket. Stir gently with a stick to quicken the mix.

In case of a spill, do not leave any sitting. Neutralize immediately by pouring baking soda.

Step 4: Turn on your pool. Even in a diluted form, changes to the pool pH should be gradual and not sudden. Large sudden changes can be a mess to the chemical balance of your pool.

Besides, you do not want the added acid to pool up at the bottom and damage the pool floor. So running your pool will ensure the pool water is constantly circulating for when you pour the acid in.

This also aerates the pool, improving the alkalinity of your pool too.

Step 5: Pour muriatic acid gently into your pool. It is best to work your way around the pool edge when adding the acid instead of pouring it at a point.

This will make it mix quickly from the edges towards the middle. To avoid contamination, always use AA specific bucket for this purpose. Be sure to indicate on it for easy identification.

Step 6: Allow to mix and then test. After adding muriatic acid, you should allow it with the pool running for at least 30 minutes to ensure it gets everywhere.

In all you do, just give it time. Then you can retest to check pH and alkalinity levels.

How do I add muriatic acid to a pool to lower alkalinity?

If the Alkalinity of your pool water is hovering above the ideal range of between 100 to 150 ppm (parts per million), then you have to consider lowering it.

Alkalinity on its own will drop down over time. But, just in case you cannot afford to wait, then you have to do it yourself.

Muriatic acid is mainly used to lower pH while lowering alkalinity in the process. Both go up and down together. This is because, though pH and alkalinity naturally are affected by the same substances, pH gets the most changes in level between the two.

But if you are looking to lower alkalinity in a pool using muriatic acid, it involves a few simple tricks to ensure alkalinity drops with a slight effect on pH. You will be using a method commonly known as pooling.

Below are the steps on how to go about lowering pool alkalinity using muriatic acid.

• First of all, adjust your pool pH, if high, to any level between the range of 7.4 and 7.6. this will make it easier to readjust the pH later on after lowering the alkalinity. This should be done before now, gradual adjustments of a couple of days even.

• Ready to adjust alkalinity? Put on your safety gear. You do not want to get muriatic acid on you. Acid-resistant wear, shoes, gloves and goggles, and respiratory protection too.

• Test your pool water to determine how much muriatic acid you are going to need to add.

• Turn Off your pool pump. To lower the effect of muriatic acid on the pool’s pH level, exposure to oxygen has to be reduced as much as possible. This means no water bubbling or movement. So keep your pool water as still as possible by turning off the pump and whichever extra features it has.

• Proceed next to add your muriatic acid. Remember to dilute it first before adding, to be on the safe side. Mix 1 part of muriatic acid for every 10 parts of water. Do not add water to acid but rather acid to water when mixing. Pour your bucket of diluted muriatic acid at the deep end of the pool, keeping away from the walls as possible, to avoid corroding them.

• Test and repeat until you get what you want. Sometimes a single dose might not get it fixed right away.

• Aerate your pool to raise the pH back up. Turn on your pumps and every other feature you have, with your return jets pointing upwards, and then run at full power.

There is one issue here with adding muriatic acid to your pool without running the pumps to mix it quickly and thoroughly. Highly acidic, muriatic acid will corrode your pool floor when it gets in contact with it when not thoroughly mixed.

The walls even are at risk, which is why it was recommended earlier to pour the acid at the deep end of the pool away from the walls.

To prevent damage to your pool floor, brush it constantly to keep the acid from settling at the bottom. Or if you feel this is too much work, run your pump for about 30 minutes after adding muriatic acid and then turn it off.

This will help it circulate a little, preventing it from settling at the bottom. Which of them is more effective? Please do leave feedback if you have tried both, we will love to hear your own opinion on this.

It is worthy to note that achieving a balanced pool water chemistry will be much easier if you use products that are formulated especially for use in a pool.

The pH decreasers which are usually products out of Sodium Bisulfate are made for this purpose. But you can still use Muriatic acid to get the job done and put just a little dent in your pocket, saving you extra cost.

How long does it take for muriatic acid to lower alkalinity?

Balancing pool water chemical levels is not a quick job, it requires patience. Especially when you are using chemicals that have not been calculated for that purpose.

Using ready-made and calculated pool treatment chemicals can save you some time, but you still have to wait cause the changes still won’t happen in a flash.

Lowering of alkalinity by using muriatic acid should take about 24 hours for it to react properly with the existing conditions of the pool water.

If you looking to balance pH and total alkalinity, it involves a bit of back and forth. So be ready to expect about 48 hours to get desired balance. That’s if you know what you are doing to the tiniest bit.

Some might take a day, others can extend to a week or longer, it’s just a matter of what level of pH and alkalinity you are, and what level is been planned to achieve.

Can I add chlorine and muriatic acid at the same time?

You should never add chlorine and muriatic acid at the same time. Together they react to form a toxic gas that when inhaled can lead to sever health issues.

To be on the safe side, if you must add another chemical, always do so at least 1 hour after adding the previous one.