ph drop in evening

[Chowder]

I believe it is normal for your PH to drop after your lights go out for the evening. But not will your light are on.

[fkshiu]

That is normal.

You can prevent it by running a refugium on a reverse light cycle (i.e. lights on at night) and/or dripping kalk at night to keep pH up.

[truperc]

Yes your ph will drop at night because you algae starts to produce CO2 instead of O2 which drops the ph. If it is a concern to you, you can dose kalkwasser to bring the ph up at night though it is not necessary.

Troy