Tom,

Any thoughts on how baking at the higher temperature would affect the accuracy of the drop checker when trying to indicate a CO2 level of 30ppm.

I made a 40dKH ref solution up having heated to 200c and mixed 90ml of this with 10ml of DI water to produce a 4dKH reference solution. I did a quick check with a Nutrafin KH testkit and it certainly given the inaccurcies of such test kits, the results did seem to be around 4dKH.

When I get time I'll probably try mixing up a new batch of 40dKH solution, having baked the bicarb of soda at a lower temp (80c - 90c) and make up a 4dKH solution from this. Then I can compare 2 drop checkers in the same tank to see if there is an obvious difference in the colour reaction.

Al