Creating A Blackwater tank with Hard Water Source?

Peat will do very little if anything to buffer down the pH. Soft water is easy to soften or harden but hard water is near impossible to buffer down without RO. The peat will release tannin and humic acids and will look fantastic just expect not to see the pH budge much if at all until you start using RO. Hope that helps.

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First thing would be to invest in a TDS meter and a way to measure your hardness. If you're going to go messing around with the water using RO then you should at the very least need to be able to measure the conductivity/TDS, that way you can cut the tap water with RO to reduce the hardness and filter with peat to add the tannins to provide a more suitable environment for your fish.

This is a very interesting article on the subject of water parameters, hardness pH etc, well worth a read IMO; http://www.tbas1.com/Exchange/The New England 11.pdf

If you already have the parrots and they're doing ok just leave things be until you get the RO running. As JK said, the peat will look nice but won't make your hard water any softer.

Is this for spawning concerns? What target ph are you aiming for?