Pronk I googled images of Eco-Complete flora max substrate. It looks like black pebbles, something heavy which will sink immediately upon placement. Substrates which will not cause alkalinity (of neutral water) are elements which float when initially added, e.g. peat moss, Catappa leaves, etc. Their saturation and eventual sinking process acidifies neutral water. Driftwood, touted on forum after forum after forum as an acidifier, does in fact
not acidify neutral water or acidic water if it has already been saturated and sunk (which is how most aquarists like it, saturated enough to sink and stay put). I’ve played with my pH monitor for many, many years, I know this. Do not associate what you are calling "tea stained" water with acidic water. As I write this I have "tea stained" water of 7.2, which is considered alkaline, which was 4.43 10 days ago. Time alone can cause water to become alkaline though the color remains. Just because wood makes your water dark does not mean it’s lowering the pH, especially if your pH level was below 7 to begin with.
You write, “The PH has been holding at 7.4 … I just tested the water this morning and it's at 8.8! … “ Please quantify “holding.” Weeks, hours, months, days? An increase from 7.4 to 8.8, in less than 1 week for example, is significant, I’d even go so far to call it a spike. And WaterLife would be correct, something in your tank is raising your pH.
But over months the increase may merely be the result of infrequent water changes. If the increase was gradual you should not have to worry that it will kill your critters, but regardless of how long the process has taken a pH level 8.8 is high for Betta splendens and you should eventually get around to lowering it, and maintaining a lower reading.
If you have come to the point where you are going to tear the tank down and switch it over to a new one then go without substrate. You can add it in slowly over time to increase the pH level to where you want it. And if you are truly a serious fish addict, invest in a pH monitor. Those inexpensive kits in PetCoLandMart are not for you.
Safe, cheap ways to lower the pH means peat moss. (I’m assuming you live in a temperate climate where you can’t rake up Catappa leaves.) A few USD purchases a cubic foot which can last for months. Do not go to stores around there that carry fish supplies, go to a gardening store and get peat that has not had any fertilizer added to it - this is important - if fertilizer has been added the packaging will clearly indicate so, as it’s a marketing gimmick.
If you are in a pinch and don’t have transportation I would suggest Oak leaves, if you have access to Oak trees perhaps in a park nearby. Surf google images if you don’t know what they look like. You want the dead ones and you’ll get strange looks picking them up off the ground, I know this. Go at sunrise, the joggers won't hassle you. Oak leaves aren’t nearly as effective as peat or Catappa, especially during the Spring (I’m assuming you are in the Northern hemisphere) after lying around all Winter. Best time to collect is during the Fall.
Diana is correct pH is not a stand alone value. Salts and minerals in the water play a role in pH level. I too suspect the substrate is releasing minerals into the water. Using reverse osmosis (RO) water dilutes levels of everything in the water, but not for long, and the pH will creep back up again. RO, distilled, and rainwater has no buffering capacity. The pH can spike, or plummet, very easily.
Distilled water = RO water = rainwater. The differences being that the latter is free (and in the Northeast USA is acidic), while distilled will cost you
> 0.75 USD per gallon, and you’re gonna have to lug it on and off the bus, 8 pounds per gallon, for your biceps.
Cheetah2 the cyber world says the pH of store bought distilled water is neutral, i.e. 7.0. But my monitor says 5.87. I trust my monitor, it’s calibrated monthly. Driftwood can naturally reduce pH if and only if the pH is high to begin with, which certainly seems to be Pronk’s case.
Pronk if you’re going to test distilled water with the PetCoLandMart kit you might get a reading of 6.0. That’s the lowest those kits read, right?
quangtm your Black water extract from indian almond leaves can do in a pinch, but extracts of anything should not be relied on in the long run. Whenever possible go with the raw product.
Here’s an interesting comparison of 5 acidifying elements
Lowering Aquarium pH ? the Most Effective Methods | Aquarist Magazine . Unfortunately neither extracts nor peat moss were used in the comparison. Had they been however, I'd bet extracts would be the least effective while peat moss would be equal to or even surpass Catappa.
Diana, slow changes may be best for certain species of fish + plants. But a species such as Betta splendens, in 8.8 water, does not need time to adapt to softer water anymore than a human breathing air pollution needs to slowly adapt to fresh mountain air. I’ve brought Gourami home from PetCoLandMart that were clearly sick. Clamped fins, white spots, the whole shebang, and plunged them straight into peat treated, very soft water of pH <6. The transformation is miraculous.
Some readers will believe I’m OCD when it comes to pH and to post such a long message. But over the years I've become an ardent believer in water <6.0 as the surest way to prevent fish from becoming sick (I work nearly entirely with bubble-nesting species however, not livebearers which require alkalinity), to quickly cure fish which are sick, and to induce spawning. Ich, velvet, fin rot, etc, just simply get dead in acidic water. Peace.