Planted Tank Obsessed
Join Date: May 2015
Location: Central Michigan
As long as it's a stable 8.0, I wouldn't even concern myself over ph.
I bought a bottle of ph-up and ph-down about 3 years ago when I first started the hobby. I've never opened either of them.
To echo DarkBlade, your ph will fluctuate drastically with those ph buffers.
Every/any amount of water you put in your tank will have to be buffered exactly right every time before it goes in your tank, including top-off water. Way to much hassle for what ph means to our modern day setups and livestock.
What are you doing that you need a ph of 6.5? If you really need that soft water, perhaps an ro/di unit is in order? Just remineralize to your prefered paramters and dump it in then top of with fresh ro/di. It would be cheaper in the long run than buying bottles of API. For smaller tanks, re-mineralizing distilled water would work equally as well as ro/di water.
Or you could use the natural organics route like Natemcnutty suggested, probably the cheapest easiest method depending on how large your tank is.
Pressurized Co2 will also lower ph very well.
Natemcnutty is also spot on for recommending purigen for tannin absorption. Works great and you can recharge it overnight with bleech-water and Prime.
All in all though, I wouldn't even worry about ph unless you know for a fact that it is causing issues. Then take natural steps in lowering it.
Now, If it were me and I absolutely needed at least a 1.5 drop in ph, I would use ro/di water in conjuction with pressurized co2. Now that's if I NEEDED that drop. I'm talking about atleast a $500 bill (the way I shop) just to drop 1.5 ph. The only way I'd ever consider that is if I had a big discus tank or some very tempermental soft-water plants to justify the cost of initial setup, if I didn't already have the equipment.
Sorry for the rant there but if your desired ph isn't absolutely crucial, I wouldn't worry about it as long as your current ph is stable.