your not testing correctly than
sand will not make just the ph go up and not hardness.after a few days or weeks it would have all been flushed out and lost its little amount of buffering capacity that it had.
1st sand will not buffer a tank for long ,crushed coral or baking soda might for few weeks sand might for a few days if any at all. sand will raise the hardness in your tank at first.you test for gh with a dropper kit so your test is very unaccurate.what measure do you get with that kit? you dont its just a general idea. you determine your water is soft hard or very hard thats it.get a proper test device than you can actually see what i am saying.your ph probably wont go up if your hardness doesnt .so i dont know why you keep going on about this.
2nd the bio load is smaller in your gio tank and your filters are probably full of crap in your rays tank which will lower the ph.do you understand this now??
3rd their is a possibility that the ash and minerals that are added to your guys tap water may naturally buffer up the water after it comes out of the tap. you must be using a low range ph test kit and a high range than?? if your using api drop testers. i think your testing wrong or just trying to be arguementative stir the pot.im just trying to help you understand.i dont want an arguement so please dont take my lack of grammar the wrong way lol