Water parameters- ph of 8.2 or RO water with coral pieces

[science-teacher]

Good morning all
I've had a long frustrating adventure in trying to achieve and maintain consistent pH for my future discus tank.

TLDR- I'm trying straight RO with coral pieces in the filter. 400g of coral pieces has given me a KH of 1 over 3 days. TDS has crept up about 20ppm. Not worried about targeting GH at this stage.

My question is, with my KH of 1, if that KH is used up by acids, will it draw upon the coral to prevent pH swings and use up undissolved coral? Or am I stuffed if my 1KH is used up?

My tap water is: pH- 8.2, kH- 6, Gh- 10

I have a 400 litre per day RO unit that I have been experimenting with.

I've tried seachem acid and alkaline buffers and targeted pH however the pH rose back to 8 in 1 or 2 days every time, seachem told me to make it work I cannot oxygenate my water which isn't ideal. It still only lasted 1 or 2 days with no surface agitation.

I've tried Kent's RO Right (AKA Continuum RO right), it didn't add any kh and very little gh, it is targeted to add TDS and not much else.

I've tried 50/50 tap and RO it causes no change in pH.

So now I'm trying straight RO with coral pieces in the filter. 400g has given me a KH of 1 over 3 days. TDS has crept up about 20ppm.
My question is, with my KH of 1, if that KH is used up by acids, will it draw upon the coral to prevent pH swings and use up undissolved coral? Or am I stuffed if my 1KH is used up?

[pitdogg2]

My personal opinion is that once you start playing with all those chemicals you have a very good chance of large pH swings. The Discus and biofilter well produce acid and soon you start chasing the pH with more and it will bounce too much for a stable pH and water parameters. Many folks have raised Discus in higher pH. I've had great luck with Discus in a pH of 8.0 with fairly hard water. They do well in a variety pH's as long as it stays stable and the water is consistent. With doing large water changes daily the chemical cost can get unbearable and almost impossible to be consistent with the water parameters.

My .02

[JamesW]

Consistency is key here, never experiment on a 90% WC.

You can mix progressively more and more RO to Tap water until you hit your desired TDS/KH/pH level (this is what I do)

As a crude handle, Calcium chloride will increase GH without changing pH and KH, Baking soda will increase pH and KH without changing GH. Kalkwasser will increase GH, KH and pH.

Your tap water (pH aside) has a pretty decent KH and GH to raise discus. Is the pH from a mature tank with a functioning filter? You might notice it settle after it experiences some bioload.

One option might be to use straight RO, Kent's RO right and some baking soda.