making a 125g to ro from tap

[utiliy]

a scenerio....i have a 125g tank with just plain tap in it...2 aquaclear 110's and 5 sponge filters-all ati -4 for 80g and 1 for over a hundred-with 9 discus and 3 bristlenose.
im wanting to expand-no room for another tank, so i went and bought the egg crate and cut it to fit....
if i was to take 80% of the tap out-and just run the ro delivery hose to the tank and monitor the tds and ph while it was filling up-would that be possible?
or is that just working to fast? all in all its faster than a drip from the delivery hose...or should i just add 30g of ro a day till it reaches its perfection.
anyone ever try this?
im wanting to get a few more discus-and the ones i have now should be pairing off soon.
i also have a 75g tank-would this be beter to try it with?

[Ardan]

It is best to mix RO + tap in an aging barrel with airstone and heater. the kh might drop and then the ph will drop also. this is not good for the fish. You need to stabalize everything before adding it to the tank.
If the ph does change drastically, then you will have to adapt the fish to the different ph a little at a time.

Do some experimenting in buckets before doing it in the tank.
measure ph and kh, also check gh

hth
Ardan