Re: CO2 tests & algae eaters

> The best method of which I am aware is to titrate a fresh sample with
> sodium carbonate (N/22). Free CO2 combines with NA2CO3 to form NaHCO3
> which is colourless in the presence of phenolphthalein indicator. The
> sample turns red at the point at which no free CO2 exists and excess
> Na2CO3 is present. It is then a matter of calculating the result. If
> one is careful, the result is fairly accurate. Free mineral acid, if
> present, will be measured in the test. The lab equipment will cost you
> a few bucks though. Seems a bit of a bother to me.
> ppm free CO2 = ml N/22 sodium carbonate X 1000/ml sample
> Dave

Either this also works with sodium hydroxide or else Dave has his chemicals
slightly mixed up.  The La Motte kit works on this principle using a dilute
sodium hydroxide solution.  I have found that the La Motte kit CO2 readings
agree very well with the table, especially when I use 10 or 15 mls to do my
KH reading & divide it by 2 or 3 to get a more accurate value (as suggested
by George) and use a pH kit that distinguishes pH within 0.1 unit.


> ------------------------------
> From: Kristof.DePaepe at rug_ac.be (kristof de paepe)
> Date: Tue, 12 Sep 1995 13:33:29 +0200
> Subject: Algae eaters in 20 gallon ?
> Hi,
> I am not very experienced with algae eating fish so here comes my question :
> What types of algae eaters will survive in my 20 gallon tank (pH 7) if I 
> only give them flake food.
> Kristof

This will depend a little on how much flake food you feed & how often you
do water changes, since both of these will affect water chemistry a little
& algae growth a lot.  It will also depend on whether you have any plants
for them to eat.  It will also depend a lot on luck.  I can't seem to keep
otocinclus alive but have great luck with ancistrus & clown plecos.


> From: "John Y. Ching" <jyching at watnow_uwaterloo.ca>
> Date: Tue, 12 Sep 1995 12:44:12 -0400 (EDT)
> Subject: CO2, pH and KH tests
> I've been following the discussions regarding estimating CO2 
> concentration using the pH and KH table with interest. I understand the 
> importance of getting accurate pH and KH measurements in order to do 
> this. I have a question about doing pH test. What I've found is that the 
> pH reading of my tank water seems to change over a wide range from the 
> time I added the test chemical to the vial and say, 10-30 seconds 
> afterwards. When I first mix the water with the reactant by lightly 
> shaking the vial for 5 seconds, I get a reading of 6.4. If I continue to 
> shake the vial lightly for another 20-30 seconds, the pH reading goes up 
> to 7.0.  Now which reading is the correct one. I assume that as I 
> continue to shake the vial, some dissolved CO2 leaves the water 
> resulting in a higher pH. But when do I know the chemical is well mixed 
> with the water and when is shaking too much? The vial is covered as per 
> the instructions (I am using a Wardley narrow range kit).
>  John Y. Ching (jyching at watnow_uwaterloo.ca)    |
>  Pattern Analysis and Machine Intelligence Lab	| 
>  Department of Systems Design Engineering      	| 
>  University of Waterloo, Canada            	| 

John, your pH value is going up since the CO2 is escaping from the water
when you shake the vial.  The initial measure is the correct one.