| In regard to the pH, I generally agree with the advice you were given not to alter the pH. It is a rare hobbyist with the skill, patience and time necessary to deal with a pond that has a different pH than the source water. All sorts of issues get involved. In your instance, as Bekko says, the issue is not the pH per se, but the reasons behind it. The low alkalinity is an issue for the efficient operation of the bio-filter. Also, pH affects the nitrifiers. At a pH of 6.4, the nitrifier community is not going to thrive.... but much of the ammonia will be in the harmless ammonium form. Adding the oyster shell to buffer is good, but I would be surprised that it causes the pH to rise to 7.6 unless you are using a whole lot of it. I suspect JR's thoughts are on target... your pH is rising considerably very quickly after exposure to the atmosphere due to CO2 escaping.
If the pH is higher due to chemical additives/oyster shell, this can create a number of issues for pond maintenance. When adjusted pH in the pond is much different from the source water, you need to be attentive when doing water changes. The larger the water change, the more important that the pH be similar. A difference of as little as 0.2 may cause irritation and much flashing by the koi. A difference of 0.5 seems to almost always result in flashing. Do not confuse this with parasites. Since large water changes are usually performed over a period of hours, the koi adjust acceptably, but I believe it is the better practice to minimize the irritation of pH shifts of this sort. If the low source water pH rises within minutes due to CO2 release as JR mentions, it is nothing to be concerned about when doing water changes. CO2 escapes so quickly it will not cause a problem. |