Low PH

[Tom Sheridan]

Hello, I'm new here & am hoping someone will be able to help with my problem. I have a 25 gal IM lagoon AIO. It is 15 months old, I started with live rock & sand from Tampa Bay Live Rock. There are 4 fish and several soft & LPS corals. 

My problem is my ph is always low. with the lights off it is 7.7 & at night fully lit 8.0 to 8.1. This has been the cause of several failed attempts with a variety of corals. I run a skimmer, use filter floss in both return chambers. I have 2 AI prime 16hd lights. 2 hygger wave makers and good flow. The co2 in my tank room is 405, so it's not the air quality, we live in a 275 year old drafty house. I dose a three part from Not a Feesh. My numbers are stable: alk 9.0, cal 450, temp 78, phos 0.1, sg 1.026, nitrate 10. 

The tank looks fantastic, I have torches, a duncan several zoa colonies, a bowerbanki all doing great, but if I add an SPS it's dead within a week or two. Several LPS have also died. I'm at a loss.

Thanks in advance for any help!

[seabass]

I don't believe it's due to pH, those numbers aren't that bad.  I really can't say why you're having problems with SPS based on what you've written here.