Testing water

[stardrop]

I've been keeping an eye on my water quality while it's been cycling, and I"ve been thinking.  I know there's a difference in SG between the night and day readings (someone explain why?), but is there a better time to check the other parameters.

Does the alk, ph, or anything else flucuate between night time and day time?

[gauthier613]

PH lowers at night for me.

[Hookup]

pH will often flux during 24 hours due to the light, and lack there of.
Alk, I do not see how this would swing during the day, this should be stable, however i'm not a chemist.
Temp might swing during the day if you have metal-halides, or keep your house cool at night, etc...
Salinity this should not change, however it will be effected by Temp, but I am unclear as to the ratio. 

I'm surprised to hear of salinity swings during the day/night cycle and would want to know what the associated temp range is for the tank over the same 24hours.  If you are swinging 10deg, 83-73 or something like that, maybe salinity would be effected... but I would say that you should notice that kind of a swing on the health of your inhabitants... large swings of ANYTHING are bad and I personally found temp swings of over 4 deg during the day to have a negative impact on fish and corals compared with the 2deg swing I currently have.

[Julie]

Ph variation at night is a chemical reaction; the corals stop consuming light and release c02.

[groan]

you guys are so smrt. i feel smarter just being digitally near you.

[Hookup]

Ph variation at night is a chemical reaction; the corals stop consuming light and release c02.

Some people, including me, put their fuge on a reverse photo-period to stabilize pH. 

PS: Julie is smart, i just quote smart people that i've heard... and sometimes I quote people I've overheard on the bus.