pH and KH changes in water supply

[dmaccy]

I have had a recent change in the water in my aquarium.

To date is has always been consistently pH7.5 and KH 3-4° (tetra test so standard).

However my last round of tests puts the pH closer to 8. I also tested the KH which came out at 3°. For info no ammonia or nitrites measured.

I then decided to test the tap water which has a pH of 7 and a KH of 1°. This has previously always been close to the tank at pH7.5 and KH of 3-4.

My questions are:
1- Can I Do anything to add stability back if tap water is now consistently at the new measures?
2- Do I do anything? The fiah are not yet showing any issues? ( flame tetras, black emperor tetras and julii cory)
3- Can someone explain the chemistry of this please and how low KH means pH is unstable?

 

[Essjay]

It is possible the water company has changed where they get your water from - or possibly all the rain we've had recently has diluted the KH of your source.

KH is carbonates and bicarbonates which react with acids. The natural tendency of a tank is to become acidic. Nitrate is acidic as are a lot of other waste products, hormones etc. If there was no KH, the pH would drift downwards over time until it stabilised at a very low level. When there is a low KH it can all be used up between water changes so the pH remains stable while there is some in the water then starts to fall once the KH is used up. Where KH is high, there is so much of it that hardly any is used up between water changes, and any attempt to alter the pH with chemicals fails because the KH reacts with the chemical preventing the pH falling.

I have 3 KH. When I was lazy about water changes years ago, my pH fell to off the bottom of the tester scale. When I was told that my low KH was the problem, I started doing weekly larger water changes to top up my KH and have not had a problem since.

Does your tank have any live plants? Most tanks have a pH which varies slightly throughout the day, but planted tanks can have a larger variation due to the uptake of acidic carbon dioxide by the plants when the lights are on, so it is important to test the pH at the same time of day.


If the fish seem unaffected, I would do nothing for now but continue to monitor things.
You could contact the water company to ask if they've changed the source of your water, and if they have if it's permanent.