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Low KH, high TDS ?

eminor

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5 Feb 2021
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France
Hello, since two months i swapped from 100% tap water to 75% rain water (15 ppm) and 20-25% tap water ( 240 ppm, GH 17, KH 11), i change 50% of water every week, how is that possible the tds show me 300 ppm (calibrated tds meter) ?

i have no rock in the tank, just plants and sand

I dose EI (magnesium, no calcium) but it seems insanely high for soft water, where does all of that come from ? thx
 
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MichaelJ

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Minnesota, USA
Hello, since two months i swapped from 100% tap water to 75% rain water (15 ppm) and 20-25% tap water ( 240 ppm, GH 17, KH 11), i change 50% of water every week, how is that possible the tds show me 300 ppm (calibrated tds meter) ?

I dose EI (magnesium, no calcium) but it seems insanely high for soft water, where does all of that come from ? thx
Yes for weekly 50% WCs given your WC water ppm's, 300 sounds really high... the WC water alone should be around ~70 ppm... even with high EI (NPK with Mg) that shouldn't add more than ~60 ppm... What are you dosing exactly and when, are you adding anything else to tweak other water parameters?

Cheers,
Michael
 
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eminor

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Yes for weekly 50% WCs given your WC water ppm's, 300 sounds really high... the WC water alone should be around ~70 ppm... even with high EI (NPK with Mg) that shouldn't add more than ~60 ppm... What are you dosing exactly and when, are you adding anything else to tweak other water parameters?

Cheers,
Michael
KNO3 15 ppm
K2SO4 20 ppm
PO4 2 ppm
MG 10 ppm
micro iron : 1 ppm

macro once a week, micro three ( total 1ppm iron)

nothing, just injecting CO2.

300 ppm could explain why some soft water plant struggle ? i also use 2hr aquarist method with turkey blaster to clean my soil every week, is it bad ? i doubt this it the cause, i take out organic waste that came out the soil i don't go deep (0.5 cm)
 

John q

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how is that possible the tds show me 300 ppm (calibrated tds meter) ?
Seems perfectly possible to me.

I use tap water that's 75ppm, dose ¾ ei (ish) and do 50% weekly water changes. Tds after water change is around 180, before water change is around 290.

We forget about "other" organics in our tank that we can't control, fish waste or plant waste e.t.c... all these add tds.
Is the 300ppm tds causing issues. Or are you thinking your issues are related to "high" tds readings?
 

eminor

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Seems perfectly possible to me.

I use tap water that's 75ppm, dose ¾ ei (ish) and do 50% weekly water changes. Tds after water change is around 180, before water change is around 290.

We forget about "other" organics in our tank that we can't control, fish waste or plant waste e.t.c... all these add tds.
Is the 300ppm tds causing issues. Or are you thinking your issues are related to "high" tds readings?
this tank have zero fish so maybe plants but i had tank with more plants that had way lower tds, i'm thinking that the high tds cause some trouble with myriophyllum species, but i'm always wrong in this hobby 😅
 

John q

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i'm thinking that the high tds cause some trouble with myriophyllum species
I'm no expert in this but suspect the plants don't care much about tds readings. Possibly the plants aren't happy for other reasons and are contributing to the tds readings you're getting.
 

MichaelJ

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Seems perfectly possible to me.

I use tap water that's 75ppm, dose ¾ ei (ish) and do 50% weekly water changes. Tds after water change is around 180, before water change is around 290.
Hi John, I can see that in a high energy tank - with high plant metabolism etc. - but not in a low energy tank - so something is totally amiss. My TDS swing during the week is 225-230 ppm after WC to 240-245 ppm before weekly WC.

We forget about "other" organics in our tank that we can't control, fish waste or plant waste e.t.c... all these add tds.
The 50% WC is supposed to take care of that and should be sufficient - but might not be in this case if there is a lot of waste piling up.

Cheers,
Michael
 

MichaelJ

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17GH alone will give you 304ppm. If you measured 240ppm your meter could be inaccurate.
Thats true and very likely if the device is highly nonlinear... but it also depends on the internal conversion factor from microsiemens to TDS - as all these TDS meters internally measures us/cm. Some use 0.64 some 0.5... With some of Hannas models you can choose :)


Cheers,
Michael
 

erwin123

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rather than a single measurement of TDS, Eminor should do a TDS profile, i.e. measure

(1) The average TDS of the rainwater+tapwater mix added to the tank
(2) The tank TDS before WC
(3) Daily TDS readings after WC

More data points will enable a better of assessment whether there is something odd going on (EI solution mixed wrongly?) , or the TDS meter is not accurate, etc.

I used TDS meter and Nitrate test to doublecheck whether my osmocote pellets are leaking nutrients into the water column -so far so good. I just noticed that Eminor also asked about Osmocote in a separate thread: osmocote, how much ? - may have to consider whether your root ferts are leaking into the water column...
 

eminor

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Got it, but what compound are you actually mixing and in what quantities vs. water volume etc.?

You should try do the "TDS profiling" as suggested by @erwin123 above.

Cheers,
Michael
i mesured with tds each one and it's correct

KNO3 :

500 ml -> 30 ml = 21.5 grams
NO3 target : 15 ppm
N: 3.3
K: 9.4
--------------------------------------

KHPO4 :

500 ml -> 30 ml = 2.44 grams

PO4 target : 2
P : 0.6
K : 0.8
--------------------------------------

K2S04 :

500 ml -> 30 ml = 18.8 grams

K : 10 ppm -> target : 20 ppm, KNO3 9.4 + 10 = 19.4 ppm
S : 4.1
--------------------------------------

Mg

1000 ml -> 30 ml = 200 grams

Mg target -> 10 ppm
S 13.19
dGH 2.31
--------------------------------------

Trace

400 ml -> 20 ml = 12.1 grams

Fe target -> 1 ppm
B 0.10
Mn 0.18
Mo 0.02
Zn 0.12
Cu 0.02
 
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eminor

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rather than a single measurement of TDS, Eminor should do a TDS profile, i.e. measure

(1) The average TDS of the rainwater+tapwater mix added to the tank
(2) The tank TDS before WC
(3) Daily TDS readings after WC

More data points will enable a better of assessment whether there is something odd going on (EI solution mixed wrongly?) , or the TDS meter is not accurate, etc.

I used TDS meter and Nitrate test to doublecheck whether my osmocote pellets are leaking nutrients into the water column -so far so good. I just noticed that Eminor also asked about Osmocote in a separate thread: osmocote, how much ? - may have to consider whether your root ferts are leaking into the water column...
i'll do, today i changed 90% of water to do a restart, 25 liters rain water (20 ppm) and 10 liters tap water (240 ppm), tds has been calibrated with HM digital calibration solution 342 ppm

day 1 :
before WC : 290
after without EI : 120
after dosing EI : ~180
 

erwin123

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i'll do, today i changed 90% of water to do a restart, 25 liters rain water (20 ppm) and 10 liters tap water (240 ppm), tds has been calibrated with HM digital calibration solution 342 ppm

day 1 :
before WC : 290
after without EI : 120
after dosing EI : ~180

Noted that there is a 60ppm increase with EI dosing- this is your weekly EI macro dose? So there will be one more weekly micro dose and that will be the 'final' ppm due to added ferts?
I just did a water change yesterday, so I can also compare my TDS profile

day1:
after WC before dosing - 120-125 (can't remember exactly)
after dosing: didn't record

day 2
after dosing: 130

Basically my expectation is for ppm to increase by about 10ppm a day.
 

eminor

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Location
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Noted that there is a 60ppm increase with EI dosing- this is your weekly EI macro dose? So there will be one more weekly micro dose and that will be the 'final' ppm due to added ferts?
I just did a water change yesterday, so I can also compare my TDS profile

day1:
after WC before dosing - 120-125 (can't remember exactly)
after dosing: didn't record

day 2
after dosing: 130

Basically my expectation is for ppm to increase by about 10ppm a day.
i dosed all macro for the week yes, micro 3 times a week so + 1 ppm, i start dosing micro tomorrow

i waited 30 min now the tds show 194 ppm, light still closed, co2 too, i think that's because the ferts are now everywere in the tank, still where does it goes from 120 to 194

should be + 47 with EI not so much ?
 

MichaelJ

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Location
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i'll do, today i changed 90% of water to do a restart, 25 liters rain water (20 ppm) and 10 liters tap water (240 ppm), tds has been calibrated with HM digital calibration solution 342 ppm

day 1 :
before WC : 290
after without EI : 120
after dosing EI : ~180

Well, that seems to add up (provided the fert dosing is what's stated above). I do no use CO2 so I dont have any practical experience with how much the TDS typically will go up day by day in an injected tank... but it now seems plausible, considering @erwin123 and @John q statements above - that is, going from 180 to 300 (120/7) = 17 ppm per day - which still seems quite high considering that your front loading all the ferts.... Maybe your adding too much CO2...The CO2 experts here can help you sort that out.

Cheers,
Michael
 

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