Alk dropping,

[carnut]

Tanks has been set up a couple years. I dose brs cal, alk and mag three times a week, water changes every three weeks. lately as in the last 2 week my alk is constantly dropping. I have not added or remove any equipment or live stock. Ater saturday water change alk was 8.0 today it is 7.2 and dropping. Any ideas why?

[kgross]

Have your corals gotten bigger? They grow in 3 dimensions so as they grow the use more alk/calcium. Do you have more coralline algae growing? Coralline alone can use up to 2 dkh a day in some tanks if it grows fast enough.

[carnut]

my calcium levels stay pretty constant with dosing only my alk is dropping.

[bertoni]

That's normal. Corals and coralline consume 2.8 dKH for every 20 ppm of calcium they consume, so calcium kits tend not to be very useful in this type of situation. You probably just need to dose more. Many tanks consume 2-3 dKH per day. You could check for signs of abiotic precipitation, which would be buildups inside pumps, most likely, or on the heater.