Help,ro And C02,ph

[sweets21]

would really appreciate some advice,my ph is 7.4,i live in a hard water area.im setting up a planted tank next week(this is my first attempt at a proper planted tank) with c02 injection which im led to believe will lower my ph,but by how much?
would the use of ro water be better or would this in conjuntion with the c02 lower the ph to much? can i use half/half ro and treated water from the start when i cycle the tank to stabilise the levels then use ro every water change? alot of questions i know,but i really want to get it right and have the best possible conditions for the fish to see them at there best.

 

[TwoTankAmin]

RO water has no kh which is what helps hold pH stable. How much co2 may drop pH depends upon the kh level. RO water has a pH of 7.0.

Do you know your kh level? Can you list your hardess (GH) as well.

 

[OldMan47]

You cannot use straight RO water for most fish. They require more minerals in their water than RO water provides. I get about 10 ppm of TDS when I use my RO and about 5 ppm of TDS on rain water. It is possible to use an RO followed by a deionizer, RO/DI, and get water in the 1 ppm range of TDS. My tap water runs over 225 ppm of TDS.
As TTA said, RO has no KH or GH to speak of and it makes a poor water to use exclusively on any tank. I use an RO/tap mix on 3 of my tanks to get my desired mineral contents using appropriate blends but straight RO means fish deaths in most cases. CO2 does drop pH in your tank, but it does the same darned thing with the time of day in a planted environment. A lake with plants has a rise in pH during the day as CO2 in the water is absorbed by the plants for growth. At night the plants join the fish in producing CO2 and cause the pH to drop. The daily pH cycling seems to not bother our fish at all. I would not worry too much about pH but would match my tank water minerals to the water the fish find in their own environment, if you can find that information. I make a gross assumption that fish thought to prefer a pH of under 7.0 probably experience a TDS of less than 100 ppm so I make up a mix that reflects that. With fish reputed to prefer a high pH, I use my straight tap water. So far this approach has worked well for me.
Note that a TDS electronic meter can be had for about $20 in the US, I have no idea the cost anywhere else.