Water Hardness, KH, Alkalinity, and TDS

[Mike Snaden]

Following a recent debate elsewhere on this topic, I have decided to post this here in the hope of clearing some confusion, and want to be marked on it by the great critic, for my work so far! So Dunc, does it make sense to you? I know that it is a bit messy, but it isn't finished yet!

Water Hardness, Carbonate Hardness, Alkalinity, and TDS.

Following recent debate, I have decided to encapsulate all of the above parameters into an article that will help clear up what each parameter is made up of, and it's function.

GH (General Hardness) is generally accepted as being a measure of Ca++ (Calcium) and Mg++ (Magnesium) ions present in a water sample.

Carbonate Hardness is the level of Carbonate and Bicarbonate buffers in a water sample.

Alkalinity is the quantity of all acid neutralising ions present in water.

TDS, is effectively conductivity, or if you like, Total Dissolved Solids.

GH and KH explained (please note that 17.86 mg/l is used below, as this equates to 1dH)
General Hardness although purely a measure of Ca++ and Mg++ ions, is actually measured as 'GH as CaCO3'. This makes no reference to whether Carbonate Hardness is present or not, but as a figure of how much CaCO3 would be present is these ions were part of Calcium Carbonate. So, remember, if it is referred to as 17.86mg/l CaCO3, this means it would be 17.86 mg/l. IF it were part of CaCO3. The reason for this is simple… In a normal pond pH, the Carbonate level will exist primarily as Bicarbonates (HCO3). As the pH approaches 10.25, the Carbonate level will exist predominantly as Carbonates (CO3). In a lower pH, the Carbonate ions take on a Hydrogen ions, to become Bicarbonate ions.
Since hard water is a result of water often permeating through limestone, much CaCO3 (Calcium Carbonate) will become become dissolved into the water. When this happens, for each 17.86mg/l that becomes dissolved into the water, there will be 7.143mg of Ca present, and 10.714mg of Carbonate ions. So, even though the quantities of each of these components are different, the Ca ions will be measured as “17.86mg/l as CaCO3â€Â

[B.Scott]

Thanks Mikey,
I think it safe to say that in general one should try to avoid staring blindly at individual components of water quality and try to see it as a whole. All parameters in water quality effect the others. The trap lays in people chasing values to achieve what it is they believe is a desired type of water quality.
Remember ORP meters? Suddenly everyone was quoting their ORP. A high ORP while desirable gives no definitive indication as to the overall quality. It may simply mean the UV after your ozone is not working (well) or you treated with Potassium permanganate the day before. It is an indication but doesn't say it all.
More recently we have started using TDS meters which I believe give a better idea as to what the "Big Picture" is in the pond but even this is just a part of the whole.
I often get a little laugh at people who buy very accurate meters like the Hanna meters and start trying to control their water to such a fine degree that go crazy because their meter measure a couple of naughts farther past the comma than they are used to!

Glad your back is better Mike!

B.Scott

[Bob Hart]

Hi Mike,

Th last paragraph where you say that "Suspended particles don't measure, so dirty water, may NOT necessarily be high TDS water!" the suspended solids here are not dissolved?

The term "dirty water" needs some more discussion I think. From past debates on this TDS subject, although not having soft water, I use a TDS meter to monitor how 'dirty' my pond water was, in comparison to the incoming purified tap water. The difference roughly being the 'dirt' in my system. This dirt being caused by naturally wind blown items such as any decaying leaves, dust, BW, any thing which will dissolve, etc, plus fish crap.

I'm guessing that you may mean anything 'dirty' in the water which doesnt dissolve and remains in suspension. Not sure what falls into this category though, as lets say our old friend blanket weed. BW catches and holds lots of things in the pond, which can decay in situ and therefore make the water unclean. Plus the BW itself breaks up, releases spores etc at differing times and can make the water look a real mess.

So which of these would contribute to TDS and which to just 'dirty water'?

[B.Scott]

I think you would difine suspend particals as anythng that could be removed with a centrafuge and therefore not being molecurly bonded to the water. Take clay for instance, put it in the water and in floats in it ans supported by it but will in time drop out and settle to the bottom.
I don't have a TDS meter yet but it would be interesting to see how adding different supstances to a pail of water might change the TDS. Clay, algae, fish waste and other things might make a varrying change to the readings!

B.Scott

[Gazza]

Hey Scott i am one of those people with Hanna meters that test to destruction and trust me it can drive you mad

You will be surprised what will make you TDS reading change either way but if you do keep you maintenance up and keep a clean system it soon settles down.

Mike i very nearly posted something similar last night about hard and soft water to see what we would get over here especially with the Boss man who know a thing or to

[B.Scott]

That was exactly my point Garry. TDS readings are influenced by so may factor this people go insane when it makes a sudden shift even though this isn't necessarily anything of great importance.
B.Scott

[Gazza]

My TDS stays exactly where it is all the time as long as i do all my regular cleaning and stuff and to be honest you soon get used to how they work.

I have mine on 24/7 along with an ORP unit so as soon as i go into the shed i can see PH,TDS & ORP so withing seconds i can see if all is OK.

Then i go and look at the fish to make sure there all still around

[B.Scott]

ROTFLMAO

[Bob Hart]

Keep giggling Scotty, I'm siding with Gazza - cos he's bigger than me!

Although I havent investigated it yet, use of a TDS meter on my growing-on pond, has showed the TDS is now 520. Incoming water is 260 and the water sparkles. Without the TDS meter I'd not know something was amiss.

If I'd been running an on-line unit like Gazza, maybe I'd have picked up a raising level, or perhaps a 1-off jump? When I get to the bottom of it (tomorrow morning) I'll let you know what I found.

[B.Scott]

Curse that Duncan, he's got that silly filter on here too! What I wrote was R.O.T.F.L.M.A.O and I get "rotflmao" instead!
Are we adults or what?
B.Scott

[Gazza]

I must admit when i see it scot it did make me giggle PMSL!!



Its a great bit of kit Bob

[B.Scott]

LOL too funny!

[B.Scott]

gazza you have mail!

[Gazza]

So do you lol so would you go down the RO route then Scott If you do you may need some new meters

[Duncan]

DOC's and POC's

dissolved orgain carbons and particulate organic carbons
eventually if left long enough most of the POC's end up as DOC's
you cannot see DOC's except early in the morning or late in the evening but you can see POC's at all time, welll maybe not in the dark

think of it this way temperary hardness or alkalinity and permenant hardness total hardness is the two combined total TDS is temp plus permenant plus everything else outside of these two that was once solid and is now totally dissolved into solution that would include DOC's but not POC's Na Sodium also sits out side kh and gh readings but will come into TDS readings because it was once solid and is now dissolved

temperary hardness has direct influence on pH where as permenant hardness has no influence at all it only matter to the fish that there is some there other wise it would suffer from brittle bones or bent/broken backs deficeint immune systems etc, but most foods have these compounds in anyway

if you can fathom these two out you can more than liley see whats going on