Can't seem to get calcium up

[nwsharksfan]

My water was consistently reading 280 mg/L Ca (even after water changes). I started adding a two part calcium and buffer daily about a week and a half ago. My water tests today:

Nitrate: 0
Nitrite: 0
Ammonia: 0
Salinity: 1.025
Ca: 360
PH: 8.4
KH: 13
Phosphate: <.25 (didn't realize API phosphate test was so useless)

I was a bit alarmed about how high KH and PH are. PH was originally 7.8 before I started adding and KH was 8. Only other thing I've done to the tank is add a phosban reactor.

I have been doing water changes (10%) about once a week using RODI water. I'm using the regular instant ocean sea salt.

I'm assuming the Ca and buffer I'm adding is leading to the increased PH and KH. How do I increase Ca without messing with KH and PH? And why aren't water changes helping increase Ca more?

The tank: 55 gal reef w/live rock. 1 toadstool, 1 Duncan, 1 ricordea, 1 clove coral, 1 xenia (came off plug and is likely decaying in the filter somewhere), 1 percula clown and 1 bicolor blenny. About 2 months old.

And just to throw in one more thing - I have a small cyanobacteria growth in one part of the tank. I am on day two of no lights. Wanted to make sure that three days without light won't cause irreparable harm to the corals I have.

Thanks.

 

[coralbandit]

Not being able to maintain Ca is often associated with low Mg.
Do you have a Mg test?
Can you get your Mg tested?

Add more flow to area with cyanno IMO and try to get some trates in tank!

0 trates (or even low trates) are often associated with cyanno(besides the flow thing).

 

[nwsharksfan]

It never crossed my mind to test for Mg. Guess I'll need to get another test kit. You're the only person that I've come across that said nitrates in a reef tank is a good thing. Though 0 to trace amounts of nitrate were ideal. I did forget to mention that I've been adding a manganese and iron supplement sporadically for the macroalgae in the tank. I understand Mg and Maganese are not the same thing. Just throwing it out there since I forgot to mention it in the original post.

Is keeping the lights off the wrong approach for the cyano? Makes me a little apprehensive when my coral puckers up.

 

[Reefing Madness]

Aquarium Chemistry: Magnesium In Reef Aquaria — Advanced Aquarist | Aquarist Magazine and Blog

 

[nwsharksfan]

Finally procured a Mg test. You guys were right. My magnesium was at 900. Adding Tech M to bring it up and will switch to reef crystals once my current bucket of salt is depleted.

 

[Marty.h]

KH of 13 needs around 450ppm of calcium to be in balance.

Aim for your mag to be around 1350

This is what I run my system at and have good growth an colouration.

 

[coralbandit]

Finally procured a Mg test. You guys were right. My magnesium was at 900. Adding Tech M to bring it up and will switch to reef crystals once my current bucket of salt is depleted.

Glad you think you have worked this out!
Keep us informed...