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Going RO (Not Making Ionic Soup)

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JumpMaster:

--- Quote from: JumpMaster on May 09, 2014, 08:34:19 pm ---I am still trying to wrap my mind around the mechanics/chemistry. You have PH, KH, and TDS.  PH is not connected to KH and TDS correct? When I create RO I will have a neutral water of a PH of 7 and the KH and TDS will be about 0. I need to mineralize the water so the fish can survive. So I want a KH of about 2 a TDS of???. The Tea, bog wood, and C02 will lower the PH. Probably to 6.7 - 6.9.

By using Aquadur after creating RO water I will achieve the desired KH and TDS and The PH will not be affected?

Am I understanding this??

--- End quote ---

I moved this from my Plec thread

JumpMaster:
I have read a about 6 articles about water chemistry and have received many explanations, but no "PH,KH,and GH for dummies".

Sacha:
I remember Vale! Giving a good explanation, so all credit to him for this.

Draw a big circle. This is your TDS- absolutely everything in the water, that is not H2O.

Draw a smaller circle within the big circle. That is your GH- "general hardness", or "total hardness". A measure of all the magnesium, calcium etc- everything in the water that contributes to hardness.

Draw yet a smaller circle within the GH circle. This is your KH- "carbonate hardness". This is a measure of all the carbonate in the water. Typically in the form of calcium carbonate, but sometimes also in other forms like potassium bicarbonate.

TDS is an arbitrary measurement. It gives a broad overview of EVERYTHING in the water. A TDS of 100 might equate to 100 PPM of calcium carbonate, or it might equate to 100 PPM of ammonia.

GH and KH give you a decent indication of the levels of minerals in the water. If fish like soft water, it means they like water which is low in minerals, so of a low KH and GH.

pH, now thats a funny one. pH doesn't really measure anything in the same way that the previously mentioned three do. pH means "potential of hydrogen", or "power of hydrogen". What does that mean? Essentially it is a measurement of the strength of ionic bonds of certain compounds, which contribute either to acidity or alkalinity.

Now pH doesn't really mean anything to us, unless we know the cause of it. Let's take a cup of water with a TDS of 100, and KH and GH of 3.

This cup may have a pH of 6, while an identical cup next to it has a pH of 2. Why? Because I squirted some sulphuric acid into the second cup.

So lower hardness doesn't always equal lower pH. There are other factors at work. What the fish care about is whether the pH drops are caused by either a strong acid, or a weak acid. They are very tolerant to pH changes, or "swings" caused by Carbonic acid from Co2, as the extra carbonic acid does not interfere with the chemical constitution of the water in any meaningful way that will effect the fish. So you can watch your pH swing up and down like a yo- yo with Co2 injection in a softwater tank, and give yourself angina worrying that it's going to kill your fish, but they won't even notice that anything has happened.

Squirt some Sulphuric acid in the tank, and it's a different story.

So really, the fish don't care about pH. They care about whatever it was that happened to cause the pH to change.

Sacha:
KH and pH have an interesting relationship. Higher KH (higher level of carbonates in the water) means the pH will be more stabilised, and will move around less. At lower KH, the pH will not only be lower, but it will also be more easily manipulated, and will vary more throughout the day. This is because the ionic bonds are weaker in water of lower carbonate content.

Mol_PMB:
Thanks :)
I'll add my two-ha'porth:

KH isn't really a part of the GH. KH is a measure of the carbonate content, while GH is a measure of calcium and magnesium (predominantly).
 
Because a common cause of hardness in tapwater is calcium carbonate, this 'scores' on both measures. But adding potassium bicarbonate (which I do to control KH) increases KH with no effect on GH and it's quite possible to have KH higher than GH.
Similarly adding magnesium sulphate (a component of EI ferts) adds GH without adding KH.

Marine fish have a lower salt concentration in their body than in the water they swim in. For freshwater fish it's the opposite. So the way the two types of fish handle water and salt levels in their body is quite different. This is called osmo-regulation.

Some families of freshwater fish originally evolved in the sea, and later colonised freshwater habitats. These families (including livebearers, rainbowfish and cichlids) are in general more tolerant of high TDS/hardness than the families of fish which evolved in freshwater.

My tapwater has pH 6.8, GH 3, KH 0.6 and TDS 40. That KH is about the maximum I have in my tanks - I add small quantities of potassium bicarbonate to maintain it around that level when necessary, but sometimes it drops to nearly zero. My blackwater tank normally runs at KH 0.2-0.6, GH 1-2, pH 6.0-6.4. I don't use CO2. The fish in that tank come from habitats with similar water, and perhaps much bigger swings in pH. As mentioned, the hardness means much more to the fish than pH within the conditions we're likely to have in an aquarium. Everyone talks about pH because it's easy to measure and is loosely linked to hardness.




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