Water paremeters

[Backer]

I have a fairly new reef tank approximately 5 months old. Currently I only have live rock and fish only. I do a 10% water change every week and use instant ocean reef crystals. My parameters have been stable since I started the tank however my carbonate hardness has recently started to drop. Currently my kh is at 6.5 dkh but has been stable at around 8 dkh previously for the last couple of months. It slowly dropped from 8 dkh to 7.5 dkh over the past month. In the last week and a half it dropped to 6.5 dkh. I wasn't concerned since my ph was always stable at 8.0 however my ph has dropped to 7.8 in the last week and a half also. Should I be concerned? Is it normal to drop that fast when no corals are present? I have not started dosing any calcium or alkalinity yet since I don't have corals yet. It also does not appear that the water changes are raising the dkh.
Tank is a 75 gallon reef with 5 gallon refugium and 20 gallon sump
Ph 7.8
Nitrate 7.5 ppm
Phosphate .03 ppm
Calcium 360
Salinity 35 ppm
Kh 6.5 dkh

 

[Spieg]

Rock and sand and coralline algae can all take up some of those components. Have you tested your freshly made SW?

 

[Backer]

No I have not tested my freshly made salt water for kh, but have tested ph and calcium. Ph only test 8.0 and calcium only 360 in the fresh made salt water which is low per the manufacturer at 1.026 salinity.

 

[Backer]

I did a water change and tested the kh of the fresh salt water and it tested 8.5dkh the ph tested at 8.1 ppm. I am also starting to grow some green algae but just on the live rocks.

 

[MaxTremors]

Do you have snails or coralline algae or anything that is growing any kind of shell, those would eat up alkalinity and calcium. Also, the bacteria in a new tank can also consume alkalinity (I’m not sure of the exact mechanism or the details as to why this is, but I’ve experienced it and it’s a fairly well-known phenomenon).

 

[Backer]

I have not seen an signs of corilline algae, nor do they have an snails. I do have some green algae growning in my refugium and I do have some cheato in my fuge, but the cheato is growing really slow. The green algae appears to be growing faster and I am seeing signs of the green algae in my tank now. I have some red legged hermit crabs in my display tank and seem to be doing well and have kept any algae at bay until recently when the green algae started showing up in my display.