citric acid

[holzdan]

hey

i noticed when im adding citric acid to my tap water to lower ph from 8 to 7 , also ppms drop from 120 to 100.
if i keep adding citric the ppms will rise again slowly , the solution tends to get more cloudy.

if i do the same experiment p.ex with vinegar just the ph drops , ppms stay stable.

i would like to understand the chemistry behind this , is the drop in ppms using citric acid maybe due to chelating properties of this acid ?

[dkeller_nc]

Yes, it's possible that your conductivity went down if the citric acid chelated some of the divalent cations in your water and precipitated them out (which would explain the cloudy appearance). But it's hard to know for sure without knowing what's in your tap water, and that would be a relatively expensive assay (at least $20 in the US).

By the way - one could lower the pH of tap water for a freshwater aquarium (though I would personally choose HCl), but there's no point in doing so for seawater.

[holzdan]

yeah im using HCL just experimenting a bit with those acids for personal interest

[holzdan]

was thinking that maybe the rise in ppms occurs when the saturation point for citrates gets reached and theres some precipitation occuring , but wouldnt precipitation mean drop in ppm ?
Possible just the organic part precipitates and the chelated CA and MAG which there is plenty in my tapwater gets back in solution again ?

[bertoni]

I doubt there's any precipitation. I suspect that that citrate is combining with metals in the tank and reducing the conductivity. That'd lower the TDS, assuming you're measuring it with a conductivity meter.

[holzdan]

hey bertoni

yes thats right first the ppms drop till i go dwon to ph 7 , if i go down even further with citric the solution starts to get cloudy looks like some precipitation and the ppms begin to raise again till i got the start EC of 120 ppm

[disc1]

citric acid is a good chelator of a number of metal ions. That binding would lower conductivity.