Can anyone help...ph question

[dw1305]

Hi all,

The TDS/conductivity can be deceiving. I now have a tank in which I haven't changed the water for about a year, maybe a few scoops the odd times when I top it up(a small tank) and the Gh, TDS and Kh have all decreased significantly.

That is an interesting question, I can see how dGH and dKH can fall, but I can't see any mechanism for TDS to fall, unless it was really high to start with, and the water really alkaline. In that case the water could super-saturated with salts, which could then potentially precipitate out as less soluble compounds.

Is my water purerer because the TDS is showing way less? Or is it polluted because I haven't done any cleaning at all?

It will definitely have more DOC and other compounds and these would contribute to the TDS, if we actually measured TDS, rather than estimating it from the conductivity. I'm a fairly fanatical water changer (small percentage change every day), and I only have very heavily planted tanks, so I never really have "old water" - <http://www.skepticalaquarist.com/bioacidification>.

cheers Darrel

 

[sciencefiction]

That is an interesting question, I can see how dGH and dKH can fall, but I can't see any mechanism for TDS to fall, unless it was really high to start with, and the water really alkaline.

The tap water is 300-ish TDS which I started with and alkaline(Gh 12, Kh 8, Ph 7.4) The TDS dropped over time. I thought at first my TDS meter was out of whack but it tests fine in the tanks I do 50% weekly water changes( they always have the same readings as the tap)
And yes, I presume the conductivity/TDS meter doesn't really measure the true TDS at all so this tank is probably loaded with organics despite the TDS readings lowering. As well as the TDS lowering from 300 to 200ppm over a year, the Gh has gone down from 12 to 7 and the Kh from 8 to 2. The Ph has remained constant 7.4 as it was to start with. Plants, shrimp and snails are doing great but they are hardy critters. Another factor that may come in place is that I recently discovered the soil that is inside this tank has peat in it which I overlooked when I was setting up the tank. Could that be the reason even for lowering TDS?

I'm a fairly fanatical water changer (small percentage change every day), and I only have very heavily planted tanks, so I never really have "old water"

Yes, I totally agree, regular water changes are the way to go. I am a water change person myself, always did 50% weekly on all tanks almost ritually but my life was a bit of a rollercoaster for the last 7-8 months(which is no excuse for the poor critters) so I left a couple of the 5 tanks that I thought can manage without much attention. They did to an extent but the chemistry went all directions as a result. Now the problem is I used to rely on the TDS meter to tell me about the tank. Now I think I can't as it maybe showing me the same reading but the tank water has gone way worse. Normally the TDS always rose over time if I skipped water changes. I never knew it can go down because of some chemical processes.


P.S. I feel I am hijacking this thread. I really apologize Michael. I hope the discussion may bring us some knowledge of how things work inside a tank.