pH jump?

[caseopia]

I'm on day 6 of a fishless cycle, and while the ammonia is only beginning to go down and nitrites are showing in very small amounts, the pH has made a large jump upwards. the water was testing at a steady 6.9 for the first few days, and i didn't test yesterday. but today it is reading at about 7.4, maybe slightly higher. any idea what might have caused this jump? I swapped filters on monday night, keeping the same cartridge so as not to upset any bacterial colonies that might have been forming. this new filter is larger and has two carbon cartridges.

ammonia- 2-3ppm
nitrites- 0.1ppm

oh yeah, and i did a large water change on monday night because i had to move the tank away from the wall a bit to accommodate the bigger filter.

 

[OrionGirl]

The water change may be responsible. You'll want to check the water you used for it's pH, and KH. If the KH is low, then what likely happened is that the biological processes (bacteria consuming ammonia) used up the KH, which reduces the water's ability to maintain a steady pH. When you did the water change, you introduced more KH, which bring the pH back up to 'normal'--when the buffer is again depleted, it will drop again. Knowing the starting values will allow you to monitor this, and either do frequent enough water changes to prevent it from occuring, or use a buffering product (not pH Up, Down or Perfect--baking soda, crushed coral, or a stable buffer that doesn't introduce phosphates will work).

 

[caseopia]

I don't have a test kit for kH, but I tested my tap water's pH- about 6.9

do I want to try and maintain the 6.9 level? if so, won't frequent water changes just continue to spike the pH each time, and harm the fish?

Would I add crushed coral to my substrate (play sand), or to the filter?

thanks so much for your help!

 

[daveedka]

Water straight out of the tap usually reads lower than it does after it has sat out for a while. elevated co2 levels will equalise and ph will rise. You probably don't want to try to maintain ph around 6.9 because that would normally indicate a very low KH tank and would be prone to crashes. Set some tap water out in a shallow bowl overnight, and then test it you will probably find it increased overnight. assuming you have enough KH, the PH you have after sitting overnight would be what you want to target in your tank.
dave