Big Trouble!!!! pH swing 8.1 - 8.7 daily

[Morgandy]

Yeah, that's correct. Morning's the pH is at 8.1 - 8.2. By 2-3 in the afternoon it is creeping higher and higher until at night it peaks at 8.6-8.7.

75gal
8 fish, 2 are 2-3", 5 are 1-2"
Temp 79
Sal - 1.024
Alk - 2.86
Calc - 390
Mag - 1280

I added T5's last week, and have been using boxes of Tropic Marine Pro - makes 50gal's, instead of the huge buckets I used previously. Have been running chemi-pure, but removed that finally. Sumpless system, no macro, Barracuda and Red Sea HOB skimmers.

I'm kinda desperate here!! Thanks for any help. Never had a problem remotely resembling this.

 

[Randy Holmes-Farley]

More aeration will reduce or eliminate the pH swing.
How are you supplementing alkalinity?

 

[Morgandy]

Randy, I'm using baking soda, and always do everything based on your calculator. There is a lot of aeration, but I'll start more. I do a lot of water changes also. I'll add a couple more pumps and report back!

thx..

 

[Randy Holmes-Farley]

The high pH end of the swing represents carbon dioxide being used up during photosynthesis. More aeration will bring in CO2, and reduce that pH maximum. Raising alkalinity will also reduce the pH swing, so you might air for 3-4 meq/L.

How are you measuring pH?