Should I bother about TDS or hardness?

Sergey

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6 Mar 2019
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Hi guys,

I've had mixed success with keeping shrimps (RCS/Tangerine tigers/Racoon tigers) and lately decided to read more about shrimp keeping to achieve more sustainable results. One parameter I stumbled upon was TDS, and the opinions about TDS values for shrimps were quite controversial.

One thing I still can't get my mind wrapped around is: when we measure TDS (for shrimp keeping), is it mostly used as a proxy measure for GH? Or TDS value itself is important for shrimp keeping?

The main reason I'm asking is that TDS in my tank is 300-350, but GH is 6-7 degrees, as measured by the test kit. Added TDS I believe comes from (among other things) ferts (EI dosing) and driftwood. So should I be ok with this amount of TDS, as long as GH is 6, or I still should try to lower it to recommended 150-200?
 

Thumper

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Well, lets get a few basics layed down.
1. GH should be around 5-6°dH
2. pH should be around 6,5
3. KH needs (for the pH to be 6,5) to be around 0-0,5°dKH
4. NO3 shouldn't be skyrocketing and NO2/NH4 shouldn't be there.

If all this fits, then its fine. Why? Because TDS is the sum of all the stuff which is in your water (ferts, GH, KH - so to say).
The thing with TDS is, that most hobbyists use RO water and GH-raisers. As RO water has literally 0 TDS, they'll raise it to ~150-200 to get the KH and GH set. If you furtheron keep plants, sure they'll need ferts - so they add them and the TDS rasies a bit, but the GH and KH (and pH) wont change (in most cases).
 

dw1305

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Hi all,
One parameter I stumbled upon was TDS, and the opinions about TDS values for shrimps were quite controversial.
It really depends upon the shrimp species, you can't <"generalize too much">.

Red Cherry Shrimps (and Amano shrimps?) don't do well in <"very soft water">, the various Crystal shrimps need relatively low hardness values. I haven't kept these so I'll let the others comment.
when we measure TDS (for shrimp keeping), is it mostly used as a proxy measure for GH?
Yes, sort of. There is a relationship normally between dGH/dKH and conductivity, because in natural fresh-water the most common ions are Ca++ and HCO3-, from the dissolution of limestone (CaCO3). It isn't always the case, but usually higher conductivity values reflect higher dGH/dKH.
Added TDS I believe comes from (among other things) ferts (EI dosing) and driftwood.
It will be the fertilisers, but it won't be the driftwood (unless possibly it was collected from the Baltic, relatively recently? and may have traces of salt).

TDS meters don't actually measure TDS (which the wood would contribute to), they measure electrical conductivity (proportional to the number of ions) and then use a conversion factor (usually 0.64) to estimate ppm TDS.

cheers Darrel
 

Sergey

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Location
Helsinki, Finland
It will be the fertilisers, but it won't be the driftwood (unless possibly it was collected from the Baltic, relatively recently? and may have traces of salt).
Hi Darrel, do I get it right that the driftwood releasing tannins will not affect the conductivity, thus won't change the measurements by TDS meter?
 

Sergey

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Helsinki, Finland
Guys, thank you very much, I think your answers cleared the issue for me.
So my current understanding is that I should focus on keeping GH/KH within recommended values and not worry about TDS value creeping up during a week.
That makes sense to me.
 

dw1305

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Hi all,
do I get it right that the driftwood releasing tannins will not affect the conductivity, thus won't change the measurements by TDS meter?
Yes, you do it is only ions that effect conductivity, and tannins etc don't carry a charge.

You can only measure the real TDS value by evaporating a <"known weight of water to dryness">.
You can only actually measure TDS by evaporating a known weight of filtered water to dryness, and then weighing the residue. Even in hard fresh water you need a pretty accurate balance (and good laboratory practice) to get a value. I've tried this a couple of times (you use a filter paper in the bottom of a beaker to making weighing easier), but I've never got a satisfactory result (the filter paper has often been lighter at the end of the evaporation process).
and not worry about TDS value creeping up during a week.
That makes sense to me.
I'd just measure TDS over a few weeks, if the plants are growing well, and the livestock seems healthy, that will give you a <"datum range"> of TDS values. If, over time you find those TDS values keep creeping up, I'd just change a bit more water.

cheers Darrel
 
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