Water Changes And The Ph Balancing?

[N0body Of The Goat]

As some of you may have read, I bought and installed a Dennerle CO2 system on Saturday, when I took back the non-aquatic plants to the LFS and got sorted with a selection of true aquatics (after some great help from the forum, I had no idea I had bought a load of plants just waiting to rot)...

As much as this has lowered the pH of Southampton water from 8.1 to 7.2 (yet to check today if it has fallen further), which will suit many fish, I'm now worried about what will be the effects on the fish when I do the first change with them present! The pH dropped 0.9 points over the space of ~50 hours, including two night periods when the CO2 was stopped, as plants use oxygen and not carbon dioxide in the dark. Considering how hard our water is (gH 260mg/l, kH 200mg/l), I've been quite shocked at how much the pH has dropped.

Should I be thinking of doing several small water changes per week, rather than one larger one at the weekend, so that the newly introduced alkaline water does not change the overall tank pH too much? Say three, 10 litre changes, the tank capacity being 250l?

Would there be much value in transferring the CO2 diffuser from the tank to the new bucket of water and then increasing the bubble rate to "silly speeds" for a few hours before adding the water to the tank?

 

[Webmoose]

Hi, I was advised by an aquatic shop to either use rain water (which naturally has a pH of 7) or buy water from a local aquatic shop - after you buy the container for about £5 (which I think is expensive) the water is very cheap. You can't store it though as you need to keep it pumped.
This could solve your problem.

 

[OldMan47]

At 260 mg/l your water is much like mine. My pH in my natural tanks does not vary much, and all of my tanks have lots of plants. The only tank that sees much pH variation is one that is supplied with CO2. It swings a whole pH number, from 7.8 to 6.8 between the morning when the timer turns on the CO2 and the evening when it is turned off again. The fish completely ignore that pH swing because it is so much like the natural pH swing that fish experience in the wild. When the sun goes down, the CO2 stops being absorbed and is produced by the plant respiration. This drops the pH over night. When the sun rises, the plants start photosynthesizing and the CO2 goes to near zero during the day. Although the time of day for the swings is different, it is a change that fish are well adapted to tolerate.
After millions of years of evolution, any fish that can't take a change of that size have pretty much died out. The ones we keep are fine with a 1 point pH swing in just a few hours. They do not tolerate a change in mineral content very well but that is another story. If you don't use chemicals to control pH, your fish won't see big swings in mineral content.

 

[N0body Of The Goat]

That sounds reassuring, thanks OldMan47!