[Marcel]

Got a 155 gal reef. Have been dosing Kalkwasser through a modified Nilsen Reactor. Doses about 1 gal kalkwasser a day for evaporation replacement.

It has been running for about 1 year now. I've noticed that the pH has slowly krept up to between 8.55 and 8.67. A small pump stirs the kalwasser every 6 hours for 5 minutes. I've turned that pump off for the past 5 days, so that the doser is adding fresh water now (To see if the pH would drop).

Still the pH remains in the same range. The corals and fish look like they are doing fine. The macroalgae is doing fine as well.

I'm using an electronic probe which i've callibrated twice now to make sure it isn't off. It seems fine. The probe is located in the outflow portion of a refugium, with macroalgaes (growing like crazy) and 24/7 light on it.

Any thoughts on what could be causing the pH rise? In the past the pH was always between 8.13 and 8.30. In the last few months it has just slowly krept up.

I'm not panicking about the high pH because everything looks like it is thriving. But this reading is a lot higher than what I've seen or read about elsewhere.

[eses]

What are your calcium/alk readings?

I noticed in my system once I started running the sump lights 24/7 and a lot of caulerpa the Ph came up and swings between 8.4-8.6. I have not had any ill effects from this. Could be similar to what is happening in your system.

My only problems with this are I have to be more careful when dosing calcium or buffering as to not raise the Ph at all as there isn't really much more room for it to go up.

[bongobrian]

I'm not sure, but I'd say it's because of all the caulerpa. It's probably using up most of the C02 in your tank causing the ph to sway to the right end of the scale.

[Randy Holmes-Farley]

Are you sure that shutting off the pump stopped the Ca(OH)2 from dissolving into the solution? Try measuring the pH of the output.

I agree with the others that the output from a refugium lit 24/7 will run high. When my refugium is lit, the pH of the water leaving it can be substantially higher than that entering it. When the lights are off, the opposite is true.

Try measuring the inlet or the tank pH just before the main tank lights come on to see how low it is getting.