Alkalinity rising quickly - Params ok?

[Brav403]

Alkalinity has risen from 8 to 10 over the last week or so. Only thing I've changed is salt brands where I did a 10% water change 48 hours ago.

Params are
Ammonia 0
Nitrite 0
Nitrate 5
Ph 7.9
Phosphates 0
Kh 10
Calcium 500

Any advice on how to stop this rise happening? Not running filter media but have Activated Carbon to hand. Filter sock probably needs a change.

Edit; i should add livestock are X2 Clowns, X1 Bicolour Blenny, X2 Hermits & a Conch. I don't have any Corals and the tank is 8 weeks old

 

[Randy Holmes-Farley]

I cannot see how the water change did it. The new salt water would need to have 20 dKH more alk than the tank water.

It may just be test error. Other causes of rising alk (e.g., nitrate falling by 43 ppm to give a 2 dKH rise in alk ) are not likely the case.