Hi all,
Would be my guess.
The TDS (conductivity) reading should be right. It is a linear scale and pretty straightforward. That is why I like conductivity as a metric, it might not be that useful, but it will be accurate.
After that It is going to depend upon what the test kits actually measure. The dKH drop test <"
measures alkalinity"> via an <"
acid base titration">, and I have no personal experience of their accuracy.
I've no idea how the dGH kit works, but if it produces a white precipitate? It may use soluble dilute sodium hydroxide (NaOH) to <"
form insoluble Ca(OH)2 and Mg(OH)2">.
You would also potentially get aluminium and iron hydroxides formed as well, although they wouldn't necessarily be white, and as the solution became <"
more alkaline the aluminium ions would go back into solution">.
But you actually know exactly how much dKH and dGH you have in your RO water, because it is
the amount you've added, it is your standard. If the test kit numbers you've got are different? It is the test kit that is wrong.
The workings are in <"
What do the three....">, derived from Larry Frank's very useful <
"the Krib"> article.
cheers Darrel
OK, so back on this one Darrel, I've been reading through some of the links you gave, though most of the real chemistry is beyond me, and the whole KH/alkalinity discussion appears to be Alice's 'rabbit hole', so I don't want to fall down that too far!
After another week of water changes, I'm still consistently measuring a KH (alkalinity) of around double what I'm adding to the RO mix, and a GH around 1.5 times. Having now read around a number of other forums, I've seen a number of other similar experiences when using large amounts of Seiryu stone. Since the whole point of me going to the effort and expense of the RO system, was to maintain soft water for soft water fish species - purely to give them the best possible environment and care, I need to establish a practical way forward, and chalk up (no pun intended lol) the extensive use of stone containing calcium carbonate as a 'schoolboy error' (next time I'll be using lava rock!).
So, at risk of wearing you a little thin on this subject, can I pose some more questions?
1. If the KH measures alkalinity rather than pure carbonate content, do we actually care - from a practical sense - about the quantity of carbonates? What I mean by that is, if the aquarium water is obtaining additional alkalinity from somewhere, in terms of providing a healthy aquarium, do we care what it is comprised of, or simply that it exists? If not, it would seem a practical approach would be to simply cease dosing K2CO3 completely, which should (in theory) mean the aquarium maintains an alkalinity of around 3dKH on its own? Are there any risks in that approach?
2. If we believe that the rock is the main culprit of the increasing GH, Is it safe to assume that the difference in dGH will be appearing mainly if the form of Calcium (I assume there is no practical way to test this)? If so, it would appear that a practical solution would be to reduce the dosing of CaCL2 by half (or more if necessary) to reach the desired dGH?
3. From a fish care perspective, is all this effort worth while - will the fish actually be happier, healthier and longer lived in the softer water? Also, my only reason for trying to maintain a GH of around 7 is so the shrimp have sufficient Calcium in the water column for moulting - is this a valid objective also, or should I just go softer on the GH (perhaps not dosing CaCl2 at all) and supplement with calcium rich foods?