low dKH...is it dangerous and how do I fix it?

Hello reefers,



I have a 50g reef tank, still new (3 months old) with some LFS and some snails & hermit crabs. No fish yet. I added a shrimp 2 weeks ago but didn't survive even if i made sure to acclimate it well.

I tested my water last week and today again. Parameters are:



ph 8.2

dKH 5 mg/l

Ca 490 mg/l

Mg 1060 mg/l

Nitrates 12

Phosphates 0,02 mg/l

Temp. 77F

Sg 1,024.5



I know nitrates are high, but they are going down with the WC once a week (10%). My main concern is the alkalinity level of 5mg/l. It has always been around 9-10mg/l and these past 2 weeks is very low. But Ca and Mg seems to be ok, so I'm confused. I have a tunze Skimmer, 20kg LR and live sand, I syphon the detritus every time i do WC. Corals look ok though. I've been thinking to add some buffer but my local reef supplier says don't do it! I use Red sea test kits and Red Sea Salts. Could it be the test fault?



I need to say that I took the salt from the original bucket to use the bucket for WC and it's been only in its plastic bag, maybe exposed to air and humidity. Could this be as well the reason for lower dKH?



Thank you for your help!