Steve... After having lost 4 Juliochromis Regani within hours of putting them in a new tank I am taking more interest in the pH of my tanks. I believe the reason the fish died was because they had gone into a tank with a pH that was too different to what they had been used to swimming in. I now keep Baking Powder and Bicarbinate of Soda at home now so that I have the capabilities of adjusting the pH either way. I do however feel a bit aprehensive in using either yet as I could see a situation where I need to, for instance up my pH so put in an amount of bicarb and then find I have put in too much so need to put in some baking powder to bring it down again. Of course I could even have to put in some more bicarb if I put in too much baking powder. In an empty tank I would not be so concerned but in a tank containing fish I dont think they would be too pleased having to try and cope with water pH going up and down.

I will shortly be having a small tank that I can experiment with that will not contain fish. Would it make sence to fill with water and add for instance 1/4 spoon bicarb and take note of how much the pH goes up? If it went up for example from 7.0 to 7.5, could I take it that 1/2 a spoon would put it up from 7.0 to 8.0? Then, if I did a 25% water change, to get the pH up to 8.0 again (assuming the new water would be 7.0) would I have to put in 1/8 spoon on bicarb, (25% of 1/2)? Also, if I used a tank of double the size, does it make sence to just double the amounts that I say.

Nigel.

Nigel,

You have raised one heck of a lot of good points here and I'm afraid that I am not 100% certain on the answers, but I will try my best.

The first thing to remember that pH is a logarithmic scale to base 10 and is about the number of free H+ ions available in the water. The other side of this coin is the number of OH- ions free in the water. When these are in equal quantities, all the H+ are (theoretically) combined with all the OH- to form H2O - 'pure' water. An imbalance make the water either acid (more H+) or alkaline (more OH-). The logarithmic scale takes over to mean that pH 8.0 has 10 times the amount of 0H- ions as pH 7.0, pH 9.0 is 100 times more, and pH 10.0 is 1000 times more.

This means that a pH of 7.5 has 10 to the power (7.5 minus 7.0) = 10^0.5 = 3.162 times more OH- ions. To go from 7.5 to 8.0 requires another 3.162 times the amount already there (inclusive of those just added). Still with me?

The doubling the tank size / double the quantity idea, however, will work, as this is down to simple linear proportions.

I have serious doubts, too, about the use of baking powder, as this is a mixture of different ingredients, some of which are not really beneficial. I will investigate this and get back to you later on this one.

Steve