How do you control long term tds creep ?

[anewbie]

Over the past 4 years my tds has slowly crept up and this kind of make sense since the water i'm adding has tds greater than 0 and some water evaporate increasing the concentration in the aquarium. Removing some water and replacing it (water change) would drift it towards the tds of the added water but over long periods it still builds up - now it is nearly 2x new water (in my case tap which is around 120).

Other than removing 100% water and replacing it all is there a good way to control tds and does it matter that tds creep up. Also with regards to breeding - is all tds equal (i.e, if a fish generally needs tds 30 or 60 to breed - is that accurate or are there components to 'tds' that have less of an impact than other components. Vaguely i think my tap for example is mostly calcium and magnesium with some other elements - tds measures all solids but are all solids created equal with regards to impact on fish (or fish breeability).

 

[MacZ]

My TDS creep down due to the amounts of emersed plants (4 pothos with a total twine length of what I estimate to be about 8 meters) and other plants (a big Nymphaea e.g.).
The past 3 months I add about 15-20 mg/l in humic substances and fertilizers with every waterchange to a desired value of 35-40mg/l. After a week to 10 days only topping up with 5mg/l RO I end up with a result of 25-29mg/l right before a waterchange.

is all tds equal (i.e, if a fish generally needs tds 30 or 60 to breed - is that accurate or are there components to 'tds' that have less of an impact than other components.

The lower the necessary values the less impact the composition has, as the singular parts reduce down to negligible amounts.

 

[anewbie]

I think i need to be more careful in measuring tds; it seems that i tend to measure it just after a water change which is also just after i add fertilizer. Probably should take a reading just before the water change and just after.

Does everyone use a tds meter and then convert to us/cm or are there actual us/cm meters ? I see you are using mg/l - i can't convert all these values

 

[MacZ]

I think i need to be more careful in measuring tds; it seems that i tend to measure it just after a water change which is also just after i add fertilizer. Probably should take a reading just before the water change and just after.

I measure pre-waterchange, post-waterchange and then again after the fertilizers have properly mixed in. I only add them after filling up. Besides measuring the RO right out of the unit every few weeks when bottling it that's all I do anymore. I noticed a slow overall decrease in readings over time with the plants growing more and more. After setting up the current tank in 01-2022 the readings were still around 50mg/l.

Does everyone use a tds meter and then convert to us/cm or are there actual us/cm meters ? I see you are using mg/l - i can't convert all these values

Mg per liter is identical to ppm. For conversion just change the unit.
Multiply by 2 and you get the corresponding µS/cm within the accuracy sufficient for a hobbyist.
My meter is actually an EC meter. The chip converts to TDS when pressing a button. It also switches between metric and imperial.

 

[anewbie]

I measure pre-waterchange, post-waterchange and then again after the fertilizers have properly mixed in. I only add them after filling up. Besides measuring the RO right out of the unit every few weeks when bottling it that's all I do anymore. I noticed a slow overall decrease in readings over time with the plants growing more and more. After setting up the current tank in 01-2022 the readings were still around 50mg/l.


Mg per liter is identical to ppm. For conversion just change the unit.
Multiply by 2 and you get the corresponding µS/cm within the accuracy sufficient for a hobbyist.
My meter is actually an EC meter. The chip converts to TDS when pressing a button. It also switches between metric and imperial.

so 100tds is 200 uS/cm or mg/l; and 30mg/l is 15 tds which is pretty low.

 

[Apistoguy52]

100ppm tds is 100 mg/L, or 200us/cm. 30mg/l is 30ppm tds, which would roughly convert to 60us/cm

 

[Mike Wise]

No, ppm TDS = mg/l. µS/cm is ~ 2X the ppm TDS or mg/l (my conductivity meter instructions indicate 1.7X). So if you have 30 mg/l (or 30 ppm TDS) your conductivity is approximately 60 µS/cm.

 

[dw1305]

Hi all,

Mg per liter is identical to ppm.

It is. One thousand mg in a gram (10^3) and one thousand grams in a litre (10^3) add the together and 1 x 10^6 is a million.

Does everyone use a tds meter and then convert to us/cm or are there actual us/cm meters ?

What ever it says on the label they are all conductivity meters, meters that estimate the amount of ions in solution by passing a current between two electrodes.

Different ions conduct different amounts of electricity dependent upon their valency, you normally assume a conversion factor of 0.64 for fresh water (100 microS ~ 64 ppm TDS) and 0.5 for salt water.

Although TDS includes non-ionic substances, these aren't measured using conductivity.

You can only measure "ppm TDS" by evaporating <"a known weight of water to dryness"> and weighing the residue.

I've done this, and it is incredibly tricky in low conductivity water.

cheers Darrel

 

[Mazan]

My TDS meter measures in ppm which as others have pointed out is the same as mg/l. Press a switch and it changes to read conductivity in µS/cm, as Mike Wise said this is about twice the value of TDS. I can also read temperature in either degrees C or F.

I don't measure every time I do a water change, but I have on occasions measured both before and after. I haven't noticed an upwards trend with time, if anything TDS in the tanks seems to have got lower in the last few months. My tap water has very low but somewhat variable TDS, today it is reading 17ppm, I have seen values between 7 and 20ppm from the tap. I just tested 3 tanks (last water change was last Thursday, no fertilizers added). Two tanks are reading 17 and one 23 ppm. I have sometimes had readings over 30ppm, but not recently.

 

[Ben Rhau]

Same as Mac, my TDS tends to creep down due to plants consuming the ions. If I observe TDS going up, it tends to be in tanks where I'm either dosing too high or there is a flow issue.

My meter also has a toggle that converts conductivity to TDS. However, as noted by everyone above, this assumes a coefficient of 0.5, which is for saltwater. Therefore, I always record conductivity and multiply manually by 0.64.

I also calibrate the TDS portion periodically with the 1413 us/cm solution and then confirm the calibration against a low conductivity standard (23 us/cm). Maybe every few months or so.

I assume you always measure your tap, right? My tap varies a lot, usually drifting back and forth between about 30 and 150 TDS. Tends to be higher when it's rainy. I think because the rain is reaching the water supply through the ground, so it brings minerals with it.

Cheers

 

[anewbie]

my head is spinning.

 

[MacZ]

my head is spinning.

Can we un-spin it somehow?

 

[dw1305]

Hi all,

my head is spinning.

Simple enough. All the "moving bits" are here <"https://www.apistogramma.com/forum/threads/ivanacara-bimaculata.24589/#post-117959">, but to summarise.

• All TDS meters are conductivity meters.
• Non ionic dissolved solids contribute to ppm TDS, but not to conductivity.
• A relatively small addition of ions causes a large increase in conductivity.
• Conductivity is a linear scale.
• Conductivity meters are relatively robust and only need occasional re-calibration.
• Conductivity standards can be made up from KCl or NaCl.

cheers Darrel

 

[anewbie]

Can we un-spin it somehow?

No - it was mostly a comic comment but a bit too subtle i think; I got the gist that these tds meters are conductivity meters that have (usually) been calibrated to salt water since different substance have a different level of conductivity and they aren't really measuring disolved solids at all. However - life would have been much more simple if they were just sold as conductivity meters and even more clever if you could adjust the calibration (though in truth that might be useless if the calibration doesn't drift). Calling them TDS meter is after all a misnomer given their actual functionality.
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Of course the unknown to me was the actual conversion factor between conductivity and displayed TDS (something i'm likely to frequently forget).