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I have just bought a conductivity meter which will automatically convert into TDS (Total Dissolved Solids) in ppm. Now I know that to convert to degrees dH, you simply divide this by 17.9, but is this result simply the TDS converted to dh, or is this value the same as GH?

If not, how do I convert between TDS and GH? (or conductivity)

Hi!

Isnt conductivity the total amount of solids? Which would mean KH+GH (afaik).
I think here the conductivity meters show results in µS (Micro-Siemens)

Thanks caol-ila,

I was under the impression that GH included KH, or is it,

GH + KH = Total Hardness = TDS?

In either case what TDS (or conductivity) value should I be after for a cory/discus setup?

Also, the conductivity reading is in micro-siemens, but my meter can convert to TDS in ppm. I thought this may be useful as I know that dividing by 17.9 will give degrees dH provided that GH and TDS are the same thing.

Thanks xsu-xsu,
I was just wondering that very thing

And I was also under the impression that TDS = GH which I thought included KH

Hi!

Sorry i was wrong i think. I cant translate the german stuff i found on google. Maybe you just do a google search to clarify it.

So we are agreed then that GH includes KH and that GH is the same as TDS?

I was thinking maybe thatGH is the amount of dissolved calcium and magnesium in water as this is what most GH test kits test for. GH, then, must include ALL ions in the water so must be the same as TDS.

Also, what KH value should I be after. I've read that 8 is what you should aim for, but I have spoken to a few people and read in other places that a KH of 3 is fine. Obviously, a lower KH would help give a lower pH, so should I be striving for no lower than 3?

Also, to re-mineralise RO water, I have been told that I shgould raise GH to around 3 first and then add sufficient KH changer (I use sodium bicarbonate which is far cheaper than the expensive manufactured liquids and does a far better job imo) to increase KH to 3 or slightly over. This would probably give a GH (or TDS) of around 4-6. Is this fine for discus and corys?

Actually, looking on the net yet again, I've found a few sites that say that TDS has little to do with GH!!

TDS embraces GH and KH as Colia originally said as well as other dissolved metals not included in GH and KH.
GH is only a measurement of all the divalent metal ions, predominantly Ca++ and Mg++.

There is a relationship between TDS and GH though especially if you are using RO water so you know exactly what is in your water!!

This whole problem came from the fact that I could not raise GH easily using Kent RO Right using a test kit. As I mentioned earlier, test kits only measure dissolved Calcium and Magnesium which normally are by far and away the most predominant divalent metals in water. However, it looks as if RO Right contains a considerable amount of other salts which do not contribute to GH. I ended up more than doubling the dosage to get a GH of 2dH!! Of course, now, my TDS value is very high, 400ppm!! I'm off to dilute this gradually!!

I was wondering about this myself and this thread has cleared up the issue. This site confirms what you concluded in your last post:

http://www.thetropicaltank.co.uk/hardness.htm