Mysterious conductance increase

[Benjamin Wilden]

Hey everyone,

I think I have a bit experience with aquaristics and water (about 15 years), but what I just witnessed is unbelievable for me.

After my holidays I tested my water in a 160 liter tank. The tank is divided by a filtersponge. On the one side were young Malpulutta, on the other side P. sumatranus most likely with offspring.

So the conductance was about 44 µS. Than I changed 10% of the watervolume by rainwater with a conductance of 18 µS (also measured).

When I came home the next day all of the Malpuluttas were dead and the P.sumatranus looked very bad, too. I put them into another tank. Two of them died later, unfortunally the only male.

So I measured again and here it comes: A conductance of 215 µS! Out of nowhere.

I have no explanation and doubt my physical knowlegde.

Does anybody have a guess?

Thank you.

Best
Bennie

[Bernd Bussler]

The only explanation I have is either the meter is faulty or defective briefly, perhaps the display has hacked or something has fallen into the water for a water change. Did you have previously washed anything in his hand, hands, or the like that you still had on his hands? :blush:

[Benjamin Wilden]

The meter is working correctly. I just calibrated and tested it.

I washed nothing with the water and used only some alder cones, which i used before, too. So I exclude them.

My fingers, yes there might have been some sweat or tap water sticking on, but does that effect 160 litre?
I never had this before, but shurely used my hands all the time 😉

Know I replaced all of the water and everything seem perfect again. But i will go on with the measure the next weeks.

[Patrick Guhmann]

Hmm, perhaps pH dropped below 4? But why?

[Tautvilas Laureckis]

PatrickG, paros can live in water even below 4 pH. So it is not an option to increase conductance if the water is “empty”.

[Benjamin Wilden]

You might be right Patrick. Conductance is effectivly the amount of ions. I never thought of the H+ ions as conductance effectors. But there are two new problems, first there must have been a dramatic decrease of pH out of nowhere, and second if that was so it had to effect the conductance that much.

Normally the conductance is mainly effected by Ca2+ ions and I think maximum about 80 µS is effected by H+, OH- and HCO3-. So this might be a part of my conducance increase but not the only reason.

[Patrick Guhmann]

at very low pH value, conductance is mainly effected by [H+]
Conductance at 25°C only [H+]:
pH µS
3,2 239
3,4 152
3,6 97
3,8 62
4,0 39
4,2 25
4,6 10
4,8 6,5
5,0 4

In your case (theoretically): 215 (cond. after water change)-44 (cond. before water change)= 171 (cond. caused by H+) –> pH 3,4

@ yankadi:
all M. kretseri died (this species does not tolerate very low pH, only 2 Paros died). I think a sudden drop of acidity (pH at 3,4) is deadly for Paros too. They tolerate very acid water, if they have enough time to adapt to low pH values. But a is deadly.

[Tautvilas Laureckis]

PatrickG,
Thank you for deeply explanation.

[Benjamin Wilden]

Thank you Patrick. You are right, my experience with “normal water” fits into your data.

Do you have any references for that data? I would like to read a bit more but can´t find it in the internet.

I just tested my rainwater and made a little experiment. I put some oak leaves and branches in and the next day the pH is about 4 at 37 µS. It seems that my water has less buffering ions than ever.

So your explanation is fitting.

[Patrick Guhmann]

The reference is:

Krause, H.-J. (2007): Handbuch Aquarienwasser. Bede-Verlag GmbH Ruhmannsfelden, 6.Aufl., ISBN 978-3-927 997-00-5(book is in German language)

If you want to know more about conductance, search for “Square-root-equation Kohlrausch” and “Wheatstone bridge”
useful link in german: https://www.uni-ulm.de/fileadmin/website_uni_ulm/nawi.inst.251/Didactics/elekleit/html/index04.html

[Benjamin Wilden]

Ok, thank you. I will order that book 😉

[Author]

Posts