Calcium Reading 0. Need Advice!

SeaHorseQueen · Jun 20, 2025

I let my tank go without doing a water change for two weeks and fed the fish very lightly. Before the water change, I tested my tank it showed 0 Calcium and 9.1 KH. After removing 10% of water, I went ahead and topped off to lower the salinity throughout the afternoon monitoring it with a refractometer. I had even added the SW mix yet. The salinity was a little high so I worked on that first. I retested and read Calcium at 0 and KH went down to 7.2. Now, I have a fresh SW mix in a bucket and it read 0 for calcium. I rinse with plain RODI water after every test and double check the directions. I hadn't even added reagent to any of the times I tested Calcium today. I haven't had issues with this salt before and it was always good. I didn't expect it to be zero calcium on a fresh bucket and I mixed it until it was clear so nothing was suspended in the water. Should I just let the tank settle and retest tomorrow or do I need to add calcium tonight?

Test: Salifert Calcium
Corals: Golden Hammer & Sunny D Zoa (growing more heads)

I did change out Phosguard and activated charcoal (grandular) tonight to help with phosphate and nitrates.

Randy Holmes-Farley · Jun 20, 2025

It is test error or misinterpretation.

Can you explain exactly what you did with the kit?

What salt mix?

SeaHorseQueen · Jun 20, 2025

Randy Holmes-Farley said:
It is test error or misinterpretation.

Can you explain exactly what you did with the kit?

What salt mix?

I added 2ml of water from the syringe that came with the kit. Then added a level scoop of the purple granules and mixed. I made sure it was fully mixed and it turned blue. It’s not a new box nor expired.

The salt is Fritz Reef Pro (blue box).

SeaHorseQueen · Jun 20, 2025

So, I made a mistake. I double checked the directions and redid the test with my tank water. It's actually at 400.

SeaHorseQueen · Jun 21, 2025

Randy Holmes-Farley said:
It is test error or misinterpretation.

Can you explain exactly what you did with the kit?

What salt mix?

Would you by any chance know why the Alk went down to a 7.2 from a 9.1 after water change? I tested my tank twice today with the same number. Would it be beneficial to do a 1-2g WC bring it back up? I did a 30% WC yesterday so I'm not sure if it'd throw the balance off by doing another WC just to increase the ALK level.