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Any expiry date on a laboratory prepared 4dkh solution

faizal

Member
Joined
1 Mar 2011
Messages
968
Location
Alor Setar , Malaysia
Hey...:). I have a couple of bottles of 4dkh solutions lying around in the cupboard...they have been just sitting there for the last 5 years:lol: in the dark,...can i still use them with a drop checker and will they still give me a reliable reading?
 
Yes and no.

4dKH water can be made using sodium bicarbonate & water or sodium carbonate & water, usually, though not always, the easier to get hold of in purer samples, bicarbonate.

The bicarbonate will react with CO2 in the air to the carbonate (not sure if it will self decompose either), probably changing the dKH value.

The carbonate solution may also absorb CO2, this altering it pH & buffering.

So in summary, fresh 4dKH is cheap, buy some more. Do you want to risk gassing your fish ?
 
I tested a bottle of 4dKH I bought in 2011 the other day (I have started using CO2 again.)

Sailfert Pro KH kit showed it was still 4dKH.

Gave it a darned good shake first though. lol
 
Hi all,
Yes and no.
The bicarbonate will react with CO2 in the air to the carbonate (not sure if it will self decompose either), probably changing the dKH value.
The carbonate solution may also absorb CO2, this altering it pH & buffering.
So in summary, fresh 4dKH is cheap, buy some more. Do you want to risk gassing your fish ?
I'd agree with Ian about using some new, but the CO2 ~ HCO3- equilibrium should mean that you can ignore CO2.

As long as there isn't any precipitate in the bottle? It should still be 4dKH.

cheers Darrel
 
Sealed it should be fine. Open to the atmosphere, the formation of carbonic acid may have an effect on the kh. As said above its cheap but also its just one of your tools to monitor CO2 levels so do not stress
 
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