9.2 PH Tap Justify RO?

[RomCOM]

I'm beginning to put together my first aquarium. Among the many variables I'm trying to make the most informed decision on (EG: substrate, filter, light volume/spectrum, etc), my tap water has stumped me the most. The API test kit for "high PH" caps out on my tap water. Looking at my location's water reports, that reading is accurate as it averages around 9 PH with regular spikes into 9.3 PH. Letting the water sit for 2 days to equalize CO2/O2 did not budge the API PH test. Granted it could have dropped it to 8.8, since that's the max reading for the test. From my reading I know that PH normally isn't too important barring specific plants/fish. I feel like those sources though are normally expecting PH more in the 6-8.5 ranges. Unrelated but my water is also relatively hard (9.95dGH) and alkaline (6.4dKH).

My concern is high PH will make any mistake on my first tank much more deadly due to Ammonia and Nitrate toxicity at that level. I'd also like lower PH as I've heard it make nutrient absorption from plants more efficient and I intended to have a heavily planted tank. Finally, a lot of active substrates buffer PH and become depleted much quicker in high PH water.

Does the above justify a move to RO/RODI water, or is there a method for handling these type of parameters that I'm just not aware of? Or, more typically of me, am I overthinking the entire thing?

Water report attached if anyone is interested or wants to confirm I have accurate numbers:

 

[hypnogogia]

If you look at the journals section you’ll see some amazing aquaria in hard water areas using tap, so your water parameters are by no means limiting. Are you planning on using CO2? That will lower ph as well.

 

[RomCOM]

My general intent is to be a no CO2 tank. Current plan is Tropica Substrate with a gravel cap and sponge filter + air stone combo for aeration/water movement. It's a 20 gallon/75 liter tank and I intend to have submerged, floating, and emersed plants at tank startup. I was considering a heater as well, a cup of water in the tanks future position read about 67f/17c which is on the low side.

On the fish side, I am planning on waiting a few months to see what the tank looked like at stable parameters then selecting a light stocking of whatever fit said parameters best. I might add some snails/shrimp earlier than that to help keep the tank under control as well.

 

[Andy Pierce]

The alkalinity listed in the report is not high enough to drive the pH over 9. I suspect they have added NaOH to deliberately raise the pH of the water. @dw1305 I believe mentioned this is sometimes done to prevent pipe corrosion? If you're comfortable measuring alkalinity it is pretty straightforward to reverse the elevated pH by adding a moderately concentrated (1M) solution of HCl. I do this with my tap water and in my case it works out to a little over 50 mL of 1M HCl to neutralise 12L of tap water. Using remineralised RODI water is a very well understood method for getting your water as you would like it for aquascaping and livestock that has a dependence on specific water parameters - that's probably your best approach other than just seeing what does well in your tap water as it comes and going with that. You would have more flexibility if you injected CO2 which will not only make your plants a lot happier but which will also decrease the pH to around (in your case) somewhere like 7.8+ as most people aim for injected CO2 to decrease pH by 1 pH unit.

 

[RomCOM]

My thoughts are similar. If I'm going to have to start making chemical adjustments to make my tap water into a workable state, I might as well make chemical adjustments to RODI water. That way I'm at least getting complete control of my water for the effort I'm spending. My local fish shop did recommend just cutting the tap with 50% RODI, but I feel then you're in a similar boat where you've got to account for the fact I'm not just diluting the PH, but every other mineral content in the water.