Alkalinity
 

So my tank is a couple months old now and I have done a 15% water change every week for the last month. I finally got around to measuring my alk and Ca. My Ca was between 400 and 450. (I didn't bother with the precision test) My ph is 7.8-7.9, but my alk is in the 3.5 dkh range. I did the test twice using my Hanna kit. Now does that alk seem plausible or should I buy a different test kit and test again before I go dosing anything.

Ya, it sounds plausible. I'd maybe retest with a different kit, but depending on salt and source water, it could be that low.

Are you sure the measurement is in dkh or in meq/l (I think that's what the other one is called)

good point. I think that value is fine for dKh...too many units for alk :)

Other way around, that's really low for dkh. :mrgreen:
If its meq/l I think it's fine.

It was 62 then 66 ppm.

Yeah that's really low. What salt are you using?

I initially used a half bucket of 8 year old IO and the rest has been new reef crystals.

Weird.

Are you dosing yet? I'd start by dosing Alk for now to bring that up to targets .. The Hanna's measure in mg/L CaCO3 which convert to dKH or meq/L as follows ..

There's also this: http://glassbox-design.com/2009/alkalinity-conversion/

.. So I think you want to target your Hanna readings to be in the 150-160ish ballpark. I think..