PH with RODI water - why is it going up??

[Linwood]

Our PH here is very high in tap water (8.6+) so I got a RODI filter.

I just filled a new large tank. I then very carefully weighed out Seachem Alkaline Buffer and Acid Buffer in a 2:1 ratio - two Alkaline to one Acid.

That's supposed to yield 7.0.

An hour or so after mixing (I have two canisters running, I put one in each in the bottom between two pads), it was 6.4, but I figured it wasn't mixed.

The next morning it was 7.6.

Today (day 2) it is 8.0.

It's a new tank. It has blasting sand for substrate, which I assume is no effect.

It has Quartzite for rocks -- yes, I'm in Florida, no I am not using the ubiquitous limestone. The Quartite was heavily pressure washed so no coating of other dust.

And the tank has one large driftwood root, bought 2nd hand from a freshwater tank. Even if it's not inert now, I presume it would drive ph down not up.

The RODI water was close to pure -- I measured it repeatedly at zero TDS while filling.

The tank is circulating but nothing active in it - no plants, fish, etc. Haven't yet started feeding it ammonia to cycle. The tank itself was new, so no old calcium deposits, etc.

I also added Equilibrium, but I HOPE that doesn't affect PH, it's not documented to by Seachem.

To get 8.0 per Seachem I needed to be off by a factor of 2 on the weights -- and I wasn't. I have a decently accurate scale, and actually did it by weight, not volume, which is what they recommend.

What am I missing here?

PS. Details on initial does: 220 Gallons fresh RODI water, 293 grams Equilibrium, 264 Grams Alkaline Buffer, 132 grams Acid buffer. Alkaline and Equilibrium added to filter #1, run for about 30 minutes while I added Acid to filter #2, and it started. Total run time now about 36 hours. No CO2 injection or such, just filtration agitation.

 

[Linwood]

A bit more info - the amounts above by Seachem's formula (unless I just can't do math any more) should result in a KH of 6, and GH of 5.

I just measured them, and KH is 9, and KH is 8.

Now an interesting aspect of this is the Acid Buffer's impact on Alkaline's KH. Their documentation says it reduces it by 0.6 dKH for each "dose", and this should be the equivilent of 6 doses. The 264 grams of Alkaline by itself would result in dKH of 9.6, the 6 doses gives -3.6, yielding 6.0 as a target.

But I did indeed end up at dKH around 9. It's as though the acid buffer did not do its reduction thing.

I'm not sure about the GH miss either. Does the acid + base buffer mixture react to form something that contributes to GH?

Or it hasn't yet -- does the reaction take a lot of time? I would assume it's just mixing time, and I've got two good-size canisters mixing the water.

 

[Linwood]

11 hours later -- ph now at 8.3, so still going up. Urged by someone on another forum I pulled the rocks out and tested with acid -- no fizz (and I used Muriatic not vinegar).

I've also got a full whiteout from a bacterial bloom, probably from the driftwood (as that's the only thing organic in the tank at the moment). Can a bacteria bloom affect PH?

 

[Linwood]

Also, I have a rubber mat in there, and wondered if that could be an issue. I had a cut piece in a glass that's been sitting for a 5 days, to make sure it wouldn't give off oil, etc. (it hasn't). I tested it's PH and it's actually lower than the tap water is normally, so it's gone down not up over time.

And, just to be thorough, I took a handfull of sand and poured muriatic acid over it and it didn't fizz at all either.