My water supply has low KH

[Deezill]

yes mine also is about 4dkh. I use Instant ocean the plain one Purple box because when I mix it my dkh is about 9.5. I dose to keep it there.

 

[Randy Holmes-Farley Verified Community Expert]

4dkh prior to mixing salt. After it goes through the filter . After I mix Red Sea blue box , it reads 7dkh.

The 4 dKH is test error then.

 

[Randy Holmes-Farley Verified Community Expert]

No problem, bet yeah don't worry about your rodi waters dkh, I use filtered water for my top offs and mixing, just checked it and it's 4dkh and I've never had an issue with dosing or my salt mix not mixing to correct values. If you want bump your Salinity up a tad to get you closer to 8dkh so you only buff up 1dkh.

That 4 dKH would be test error. True 4 dKH water would have substantial TDS.

 

[Sgolden]

That 4 dKH would be test error. True 4 dKH water would have substantial TDS.

I used 2 different kits. I did get the information I needed . Probably, my water supply runs slightly acidic during parts of the year. Couldn’t that effect a dkh reading to be lower ?

 

[Randy Holmes-Farley Verified Community Expert]

I used 2 different kits. I did get the information I needed . Probably, my water supply runs slightly acidic during parts of the year. Couldn’t that effect a dkh reading to be lower ?

you got misinformation.

Ro/ di water at 0-1 ppm tds will not have any detectable alkalinity or acidity (meaning negative alkalinity).

Fresh water with an alkalinity of 4 dKH must have a tds of at least 50+ ppm tds. There’s no way to have alkalinity and not have lots of tds.

Then, you mixed it with the salt mix and got the normal alk for that mix, meaning it couldn’t have been 4 dKH before adding the salt (unless the very unlikely scenario of a 3 dKHbatch of salt mix is being considered ).

 

[Randy Holmes-Farley Verified Community Expert]

Are folks understanding that ro/di is expected to have no alkalinity?

 

[Copingwithpods]

That 4 dKH would be test error. True 4 dKH water would have substantial TDS.

My mistake it was supposed to say 2dkh not 4, and yes I would assume it has some tds as I was testing filtered water not rodi.

 

[Randy Holmes-Farley Verified Community Expert]

My mistake it was supposed to say 2dkh not 4, and yes I would assume it has some tds as I was testing filtered water not rodi.

what does filtered water mean?
Tap water can certainly contain substantial alkalinity.

 

[Copingwithpods]

what does filtered water mean?
Tap water can certainly contain substantial alkalinity.

Regular drinking water (bottled) or from refillable 5g jugs

 

[Randy Holmes-Farley Verified Community Expert]

Regular drinking water (bottled) or from refillable 5g jugs

OK, that may have alk in it as sodium bicarbonate is a frequent additive in bottled drinking water.

 

[Miller535]

Are folks understanding that ro/di is expected to have no alkalinity?

Meaning a DKH of 0?

 

[Sgolden]

All of this is good info. From what I am hearing, in my case, city water supply. Comming into my house, filtered in a 7 stage w/ 2 ro / 1 di filters. My alk test is 4kh prior to mix.

I’m being told this is a miss read by 2 separate test kits or it’s not filtering enough.

My mixed water is testing at 7kh when at 1.025. In my case, I added buffer to the mix to reach 9kh prior to the use in my tank.

I wasn’t aware what a pre mix reading should look like . Something I must look closer at.

 

[Copingwithpods]

Meaning a DKH of 0?

If it is truly just H20 the pH should be neutral (7) therefore it's shouldn't be alkaline

 

[Sgolden]

I would be interested what other kh readings are of filtered fresh water prior to mix and mixed water kh without additional buffs.
If I’m reading 4kh fresh , adding salt which is suppose to bring kh to 8 but only reading 7kh, something isn’t adding up. I would think starting with 4kh, adding salt would make my mixed water kh higher, like 9-10.

 

[Randy Holmes-Farley Verified Community Expert]

Meaning a DKH of 0?

Yes

 

[Randy Holmes-Farley Verified Community Expert]

I would be interested what other kh readings are of filtered fresh water prior to mix and mixed water kh without additional buffs.
If I’m reading 4kh fresh , adding salt which is suppose to bring kh to 8 but only reading 7kh, something isn’t adding up. I would think starting with 4kh, adding salt would make my mixed water kh higher, like 9-10.

The ro/di reading is in error, assuming the ro/di is functional.

doesn’t matter what your kit claims. If it is 0-1 ppm tds water, it has ZERO alkalinity.

 

[Sgolden]

I will figure this out and report

 

[Miller535]

Yes

I did not comment on this thread, but I also didn't know this. Good to know, thanks.

 

[Randy Holmes-Farley Verified Community Expert]

I did not comment on this thread, but I also didn't know this. Good to know, thanks.

let's explore that in detail.

Suppose that you have fresh water with an alkalinity of 1.0 dKH (0.36 meq/L).

It must have either

0.36 mM hydroxide (OH-)
or
0.36 mM bicarbonate (HCO3-)
or
0.18 mM carbonate (CO3--; carbonate carries two units of alkalinity)

There must also be counterions present since one can never have just negative charges in water.

Let's assume it is sodium, which is most likely, but the assumption doesn't matter much. In each case, we will have a total of 0.36 mM sodium to balance charge.

How conductive are each of these solutions? We can look them up.

0.36 mM (14.4 mg/L or 14.4 ppm) sodium hydroxide has a conductivity of about 31 ppm TDS
0.36 mM (~30 mg/L or 30 ppm) sodium bicarbonate has a conductivity of about 20 ppm TDS
0.18 mM (19.1 mg/L or 19.1 ppm) sodium carbonate has a conductivity of about 20 ppm TDS

Thus, if the RO/DI water has a TDS of 0-1 ppm, it really cannot have anything close to 1 dKH of alkalinity. Maybe 0.05 dKH max for 1 ppm TDS.

 

[Miller535]

let's explore that in detail.

Suppose that you have fresh water with an alkalinity of 1.0 dKH (0.36 meq/L).

It must have either

0.36 mM hydroxide (OH-)
or
0.36 mM bicarbonate (HCO3-)
or
0.18 mM carbonate (CO3--; carbonate carries two units of alkalinity)

There must also be counterions present since one can never have just negative charges in water.

Let's assume it is sodium, which is most likely, but the assumption doesn't matter much. In each case, we will have a total of 0.36 mM sodium to balance charge.

How conductive are each of these solutions? We can look them up.

0.36 mM (14.4 mg/L or 14.4 ppm) sodium hydroxide has a conductivity of about 31 ppm TDS
0.36 mM (~30 mg/L or 30 ppm) sodium bicarbonate has a conductivity of about 20 ppm TDS
0.18 mM (19.1 mg/L or 19.1 ppm) sodium carbonate has a conductivity of about 20 ppm TDS

Thus, if the RO/DI water has a TDS of 0-1 ppm, it really cannot have anything close to 1 dKH of alkalinity. Maybe 0.05 dKH max for 1 ppm TDS.

That makes sense. Thank you