What is his water hardness ( KH) ? If he has hard water it will go up as soon as he adds some O2 . Has he ran just plan water in his res over night to see if it goes up without fert? He can get a test kit at petco for about 10 bucks. Then he will know if a RO will help. Chems hold ph better so he might not have had to use RO. My water is very hard it comes out at 7.3 ph KH over 15 and dissolved O2 of 4 after the O2 gets to 9 the ph is at 8.3 same as saltwater. Also as Ammonia drops ph goes up so if the BC pro has any in it and his res is over 30 days old ( cycled) , just like a fish tank bacteria take over and brake it down. As the ammonia starts to drop the ph goes up and will till most of it is gone, at first. If the KH of the source water is high, finding another source for some or all of the res water may be necessary. Since Reverse Osmosis water has a KH of near zero, mixing it with source water will drop the KH proportionally - in other words, using half R/O will drop the KH by half. When buffers are gone, pH begins to drop; when pH drops near 5.5, bacteria shut down and ammonia and nitrite shoot up so to low of a KH is also bad. You can use ph down all day long but it will not hold in hard water its a fight it can not win. On the up side most organics have a ph of 3 ish, so that it stops the bacteria or it would blow up in the bottles. So if you just add something with a low ph like earth juice or hope the full recipe will have what is needed, if KH is not to high it might hold. Bag of peat moss with a air stone by it will drop PH and give the bacteria a nice home so that its not all over the res making a mess. Just have to mess with how much to use and it will drift a bit. Good luck
The more you learn the more you see you don't know shit.
