Discussions like this often left me very confused in the past (my fact or fiction scenarios) that it really betrayed my confidence in what I was doing (which was soul destroying) because there are sooooo? many variations as to what is correct (in their own way, they are). However, what I have found out through correspondence is that ?municipal/tap? water parameters are not always the same for a hobbyist in South Africa compared to England, America Germany and Singapore for example. So trying to replicate some one else?s formula ?based? on their success using their municipal water parameters (not ours) was a big mistake and deserved to have my wrists slapped by Dirk?lol. (I say this with up the most respect?thank you) So it all depends on the quality of the tap water in your area to begin with But the question that I needed to ask was ?What part of the Amazon water do I need to duplicate that my particular wild/strain will be happy and breed in?? or How can I safely change ?my tap? water to these conditions or best suited for my discus. I?m sure from reading the you would have discovered 101 ways to make this happen and in my case ?.101 ways to kill a discus If one decide to dose with acid to reduce pH (of your target) you will shift the equilibrium towards the ?acidic? side in relation to the amount of acid used, but the calcium and magnesium ?KH? (Ca2+ and Mg2+) does not ?really disappear"? it is still there, maybe less then originally. This shift to a lower pH may trigger them to pair or spawn but with low fertilization thus a low hatch percentage or non, but having said that, if your tap has a KH less than 6 (reading from ones test kits) a higher percentage could be achieved but by using ?less? acid (to reach your target). So in here there can be a few variables to ones formula and this can also get tricky because tap water sometimes change from time to time? So in summary, acids will lower your pH, and since ?most? test kits that test for hardness are actually measuring alkalinity, your hardness would appear to decrease when adding an acid but in fact it would have remained the same. With an RO (which is necessary), this will remove Ca2+ and Mg2+ ?etc, thus lowering your pH with little or zero KH (buffering) you could get a lot of pH swings which can general make it not safe ?but? near perfect for fertilization, so the birth of a formula (one of millions in the making) for a good criteria, that can work for you but may not work for some one else. So my questions I need ask, regarding the usage of a pH meter. How would it measure pH? meaning? does it measure in relation to the amount of Ca2+ and Mg2+ in the water or the alkalinity? The second question, the usage of a conductivity meter, here I understand the fundamental basics but the way I understood, is that TDS and Total hardness are not the same but completely different? Total hardness refers to the hardness mainly due to calcium, magnesium, (Mg2+, Ca2+) and TDS is a measurement of dissolved solids in water and is normally based on a conductivity measurement which is converted to a value in ppm or Mg/l. So as I understood it, a TDS measurement is incapable of distinguishing between monovalent or polyvalent ions such as sodium, chloride etc and is not a reliable measurement of the true water hardness. What would be the best way to measure true KH?