Which pH buffer to use?

[abrage22]

I know it's usually frowned up on this site to use pH buffers, but I feel like it could really make my situation easier to deal with.

I'm going to set up a divided 20 gallon for 4 bettas. My tap water
1) Is very high in nitrates straight from the tap
2) Has a really high pH (High 8's)

Even with regular, large water changes, the nitrates are consistently very high. This is with me using about 75% RO with 25% tap!
I used the GH and KH API test, and came up with the conclusion that I should be using much more tap than just 25%, since the test showed that my tap doesn't have much buffer to it...And RO has really NO buffer to it...

So in order to get my nitrates down, I want to do 10% and 90% RO. I want 10% tap just so theirs minerals in the water. And doing only 10% will hopefully get my nitrates way down. And I figure if I use a pH buffer, even with a large % of RO water, that my pH won't fluctuate much...

So I don't really have a problem with the high pH, its just if I'm going to use 90% RO water, it needs to be buffered somehow...right?

So if that all makes sense, and you don't have any better ideas, then what buffer do you recommend?

I'm wanting to choose from any of these:
PH Buffers

THANK YOU FOR YOUR HELP

 

[molliwopp]

So youre using 75/25 ro to tap and youre getting nitrates in the 80s and your ph is in the high 8s? I actually think that the api nitrate test is inaccurate. Im no pro in ro water but isnt that abit high for a 75/25 mix?

Whats your ph/nitrate results of the tap water only? and have you tested the ro water?

 

[abrage22]

So youre using 75/25 ro to tap and youre getting nitrates in the 80s and your ph is in the high 8s? I actually think that the api nitrate test is inaccurate. Im no pro in ro water but isnt that abit high for a 75/25 mix?

Whats your ph/nitrate results of the tap water only? and have you tested the ro water?

Yea it is high for a mix like that. That's why I feel like I have to go 90/10%...
Tap only, ph is 8.4-8.8, nitrates straight from the tap is about 40ppm. And that's before it even gets into the tank. I don't overfeed, and I'm definitely not overstocked...