TDS + immediate dose

JoshP12

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I am slowly accumulating the toys that we all have and the most recent was a TDS meter. On its own, it doesn't tell us much, but in conjunction with all of our other tests, I think there is some merit ... or if only to confirm for the first few times that we do add to the tank is actually getting added in the way we think.

(I know the following TDS is too high and am in the process of balancing some nutrients and fixing it in the aquarium -- if anyone wants to weigh in, I'd appreciate that too).

My TDS meter read about 807 ppm and then upon adding some of my homebrew potassium sulphate solution it shot up to about 880 ppm ... does that mean that I dosed about 70 ppm of potassium :banghead::banghead: ?!?!?!?!

Side note: I usually measure it out properly but was in a rush during preparation and just threw in a chunk this time -- the excess SHOULD have precipitated out ... but I see no precipitate in my bottle. I am not worried with a high dosage of potassium based on the things I have read on this forum, but I don't want to waste the salt.

Cheers,
Josh
 

jaypeecee

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My TDS meter read about 807 ppm and then upon adding some of my homebrew potassium sulphate solution it shot up to about 880 ppm ... does that mean that I dosed about 70 ppm of potassium :banghead::banghead: ?!?!?!?!
Hi @Plants234

According to my calculations, you added close on 22ppm of potassium. I'll re-check my calculation and @dw1305 will correct me, if I'm wrong.

BTW, welcome to UKAPS!

JPC
 

Zeus.

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the excess SHOULD have precipitated out ... but I see no precipitate in my bottle
It only precipitates out when the water is saturated ;) the saturation point is mineral, temp and other minerals in the water dependant also- also think pressure has an effect on the saturation point also as this effects the boiling point of the water too :angelic:
 

JoshP12

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Hmm... I’m not surprised that potassium concentration will affect uptake tank of other nutrients —> I suppose experiment and try to find a balance ... more and more I want to do a giant water change with the balanced nutrient distribution that I want ... but I think it should do several mini ones instead slowly finding that balance.

@jaypeecee thanks for these responses: could you show how you deduced 22ppm from a 70ppm tds increase?

@Zeus. I did boil the solution and felt certain that it would be super saturated, but I guess not!!
 
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jaypeecee

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Hi @Plants234

You'll have to forgive me for using old terminology. But, here goes:

Atomic weight of potassium (K) = 39
Atomic weight of sulphur (S) = 32
Atomic weight of oxygen (O) = 16

I have assumed that you used the anhydrous version of potassium sulphate, i.e. KSO4*. So, total atomic weight = 39 + 32 + (16 x 4) = 135. Thus, the proportion of potassium (K) is 39/135 = 0.3. Therefore, total potassium is (880 - 807) x 0.3 = 73 x 0.3 = 22 (within a gnat's whisker).

It would be nice to get this confirmed by someone else but that's how I arrived at the result that I posted.

JPC

* EDIT: please see my next post in which I've hopefully corrected the error above.
 
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jaypeecee

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Hi @Plants234

I have just spotted an error in my calculation. Potassium sulphate is, of course, K2SO4. So, the corrected figure will be twice my previous figure, i.e. 44ppm.

Sorry about that!

JPC
 

Zeus.

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K2SO4*. So, total atomic weight = (39x2) + 32 + (16 x 4) = 174. Thus, the proportion of potassium (K) is 78/174 = 0.45. Therefore, total potassium is (880 - 807) x 0.45 = 73 x 0.45 = 32ppm potassium (K) approx

Think you forgot the increase in the total molecular mass @jaypeecee
 

dw1305

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Hi all,
My TDS meter read about 807 ppm and then upon adding some of my homebrew potassium sulphate solution it shot up to about 880 ppm ... does that mean that I dosed about 70 ppm of potassium :banghead::banghead: ?!?!?!?!

Side note: I usually measure it out properly but was in a rush during preparation and just threw in a chunk this time -- the excess SHOULD have precipitated out ... but I see no precipitate in my bottle. I am not worried with a high dosage of potassium based on the things I have read on this forum, but I don't want to waste the salt.
Welcome. Don’t to worry too much.

The “ppm TDS” measurement you get from TDS meter isn’t exactly what you might think, it is actually an electrical conductivity measurement, from which ppm TDS is estimated. How salts (as ions) effect conductivity depends upon the salt, I don’t know the exact values for K+ and SO4–, but I can find <“them”>.

Potassium salts are all soluble, so you won’t get precipitates forming until you’ve added a lot. When I say a lot we are talking solutions much saltier than sea water.

Cheers Darrel
 

Zeus.

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Hi @Zeus

Thanks for that. The important thing is that @Plants234 now has an answer to the question posed.

JPC
You did all the work M8 I just checked your maths and spotted a error- without your post I would of forgot how to do it withouting a google ;)

and like Darrels says above a TDS pen is not an absolute measure of the ppm anyway so could be 22 or 44ppm anyway :lol:
 

JoshP12

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@jaypeecee @Zeus. thank you both!

For what it’s worth, I totally forgot about sulphate contributing to the tds! Our calculations are correct!!

Here was mine after some thought and using all of your data:

molar mass of potassium sulphate: 174 g/mol
Molar mass of potassium contribution: 78 g/mol

percent contribution: 78g/mol / 174 g/mol = .448 ~ .45 (same as yours)

concentration in ppm = mg of solute/ litres
73 ppm (tds increase) = mg of solute/37.8 litres
mg of solute = 2759.4
mg composition of potassium = 2759.4 mg * .44
= 1236.97 mg

Then back (that much potassium dissolved in 10 gallons of water) ... 1236.97 mg / 37.8 L = 32.7 ppm

I hope it’s ok I shared my computations too - just in case they are not sound.


Thanks a lot :)!
 

JoshP12

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@dw1305 @Geoffrey Rea
Too high for what?
Well this is where I started thinking after reading both these posts --> it seems natural that between water changes my tds goes up ... and based on the fact that my water change water already has a 400+ PPM TDS just with remineralizing to KH 4 and a bit of magnesium that I don't think it's really that bad for the fish and plants.

I do not use RO; my TDS out of the tap is about 160 ppm.

I don't need to stress over this, eh?

There comes out the Canadian ... haha.
 

Geoffrey Rea

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TDS here is over 400ppm out of the tap. Until there’s a problem there isn’t a problem. Not to be coy and all for understanding, but data is just data without context.
 

jaypeecee

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Hi @Plants234

So far in this thread, we don't appear to have mentioned fish or any other tank inhabitants. In view of my errors above, please double-check my conversions that follow. I reckon that 800ppm TDS is around 1250 microSiemens/cm. I keep my tanks at 400 - 550 microSiemens/cm and I have softwater fish. Even then, my figures are a tad on the high side. I certainly wouldn't want to keep them in harder water such as what you are now seeing. But, you say that the TDS from your tap is 160ppm (250 microS/cm). So, one question is - which fish and/or invertebrates do you want to keep?

JPC
 

JoshP12

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@jaypeecee

The inhabitants are 7 neon tetras and 2 rainbow gobys ... which require very different parameters --> have made lots of mistakes on this tank so far.

my tds meter measures in microS so yep your numbers are on (I converted them to ppm for this post).

The tetras have been really healthy overall (except today I noticed a bit of rapid gasping because I upped my co2 ... reduced it just now, just a bit, and will observe what happens).

edit: healthy now!

If this thread gets too far from the original post, just let me know.

Josh
 
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dw1305

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Hi all,
Then back (that much potassium dissolved in 10 gallons of water) ... 1236.97 mg / 37.8 L = 32.7 ppm
That looks right. You can always check with the <"Rotala Butterfly nutrient calculator">.
my TDS out of the tap is about 160 ppm.
and based on the fact that my water change water already has a 400+ PPM TDS just with remineralizing to KH 4 and a bit of magnesium
I'm not sure about this. I just can't see how your TDS has risen that much with just the addition of the salts to raise dKH? From <"James' Planted Tank">
1 dGH = 7.2mg/l Ca++
1 dGH = 4.3mg/l Mg++

1.5g NaHCO3 in 25 litres of water = 2 dKH
1.8g KHCO3 in 25 litres of water = 2 dKH
1.2g K2CO3 in 25 litres of water = 2 dKH
The tetras have been really healthy overall (except today I noticed a bit of rapid gasping because I upped my co2 ... reduced it just now, just a bit, and will observe what happens) edit: healthy now!.
Do you have a <"drop checker">?

cheers Darrel
 

JoshP12

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@dw1305

For context: my kh out of tap is almost 0. I buffer kh up to 4 dkh with sodium bicarbonate (have potassium bicarbonate on the way so I don’t overload my tank with sodium) and for that last test, I had also added 5 ppm of magnesium sulphate pentahydrate (epsom salt) for my GH.

Drop checker in mail right now! I have been doing ph kh tests to cross reference.

I also contacted the people who sold me the ph and tds pen ... they may be faulty ... sigh ... new ones on the way.
 

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