Well, a few weeks back I changed my substrate to Fluorite and setup a DIY
light system over the tank that can supply 1x23 to 4x23 Watts of Daylight
(5000k or 6500k) to my 25 gallon. At the time, the tank was stocked as
follows:

1 adult + 2 juvenile platys
4 neon tetras
1 ghost shrimp
2 asian ambulias
1 java fern
1 corckscrew val
2 moneywarts
1 parrot feather
1 ludwigia repens

The tank also has 2 pieces of mopani wood that used to give the water a
yellowish tinge.

When the cloudiness of the water (due to the new fluorite) dissipated in the
following 72 hours, the water became crystal clear with no yellowish hues. I
thought this was odd because I had reused the old water after changing the
substrate. To my surprise, the chemistry of the water had also changed,
becoming softer and more acidic!

Before adding the fluorite, my tank water had the following parameters: kH =
3, gH = 3, pH = 7.8
After changing the substrate, I was measuring the following params: kH 1,
gH = 1-2, pH = 7.0

Needless to say, I lost a couple of neons in the process which I initially
though was due to the SS in the water after the substrate change, but now
believe is due to the resulting change in chemistry.

At the time, I wasn't sure if the change in tank water chemistry was going
be last, so I monitored carefully. Unfortunately, I was recording pH swings
between morning and evening (probably because of CO2 production at night),
and signs of distress in the fish. I decided to do something about it, so I
started adding sodium bicabonate (baking soda) to rase the kH to 4.0-4.5
dkH. Lately, I have started adding CaCO3 to raise the general hardness by
one or two degrees.

Fluorite is not supposed to change water chemistry. Anybody else had this
experience after adding Fluorite?


OT:
I had to increase the kH of the water to stabilize the pH. But is my 4.5 dkH
target too elevated? How about gH, should I continue targeting 3 dH?

I currently use DIY CO2 injection through an air stone. Unfortunately, I
can't achieve 10 ppm because of the mixing produced by my Dynaflo 3 power
filter (350gph!!). But that'll be replaced in the near future by a canister
filter with a spray bar.