my friend's tank is having problems. he has lost several fish in the last few weeks. 55 gal. sand substrate. around 50 lbs. of live rock. aqua c skimmer, mag filter. sp. 1.023, all other levels at o. the ph which has normally been at 8.0 in the morning and 8.3 during the day has dropped. around 7.7 in the morning and only raises to 8.0 during the day. the set up is nothing fancy. no sump or anything. just fish only. the ph is the only thing that is out of whack. could this be the cause of all of his problems? how could he easily fix this? add more sand? buffer? at this point the only thing in the tank is a crab. any help would be appreciated.