Low KH - Why and How to correct?

[rwm555]

I am having a hard time keeping my KH above 7 in my reef tank. I have about 13 corals and 5 fish.

Does anyone have any suggestions?

Here is my data.
Mag=1200
PH=8.2
A, Ni, Na=0
Cal=480

I dose calcium twice per week and KH buffer twice per week. I only use a PH buffer on water for my bi-weekly water changes. I also add Strontium, Magnesium, PurpleUp and Fuel once per week.

The tank has been running for about 12 months. During the first 9 months, the KH was always between 9 - 11.

Other facts; I have been having a problem with brown algea on the substrate / rocks and I have been having skimmer issues for weeks.

One LFS suggested that I add PH and KH buffer to my top-off water. Does anyone else do that?

 

[Myteemouse]

I use buffer in my top off and water change also cause my RO/DI filter strips it down to about PH 7 or so!

 

[Herefishyfishy]

How large is the tank, what is your filtration and water change schedule?
The low PH and KH is most likely the result of having that many fish exceeding the system's filtration/water change capability. Purple up is a pain and frequent dosing should not be necessary unless you are growing massive amounts of coral.

Need to either get a better skimmer, a larger refugium, more frequent water changes, or live with a lower PH and KH in a fish only type tank.

 

[jezzeaepi]

In short, your corals are using alkalinity faster then you are dosing. Since you are using two different products to dose, you are not dosing ina "balaced" manner, which makes it appear that alkalinity is "staying low" when in reality, you just arent dosing enough. Youll want to consider switching to a two part additive, and if your corals continue to grow, youll want to start dosing kalkwasser, or doing a calcium reactor.

The long explanation:
http://reefkeeping.com/issues/2007-04/rhf/index.php