Converting 20Gal. Cichlid tank to a S.Amer. tank

[Crepe]

Hello, I'm both new to this site and also to planting. I've been keeping fish for almost 10 years now and have mostly been working on my 600 gallon outdoor koi pond, holding 2 20" koi and several goldfish, a cory, and 2 buenos aires tetras (amazingly they survived this winter's chills in Texas [the water reached around 40F]) and they've all been doing well for about 4 years.

I'm currently now thinking about converting my 20gallon Mbuna tank housing an ice zebra, auratus, and jewel cichlid into a planted S. American tank. I've already selected my fish species at my local LFS but I have several questions:

1.) I need to convert the hard water 8.4ph at the moment, to around 7.0ph. Can I do this by doing a large, 50% water change and then running CO2 through the water for a week or so to acidify the water? I don't really want to reset the aquarium and recycle it. I'm thinking if I acidify the water over a long enough period of time I can let the bacteria acclimate to less than auspicious conditions. (Through my experience i've found that bacteria like harder more alkaline water.)

2.) Can I leave the crushed coral in the tank and just layer over a bedding of fluorite substrate? Or do I have to tear up the bacteria beds that have already set in. I know I'm going to take out the limestone and conch shells inside.

3.) What plants are good for a beginner? Being still a student, I don't have much time for maintenance. I've had good experiences with Vallis. Anacharis and Apongetons before but nothing very fancy. I'm very interested in Java Fern and growing out a patch HC or some kind of foreground plant. I might just get a batch of java moss instead. I also have a 2L CO2 reactor built already that's running up through a pipe directly into a powerhead.

Any tips?

 

[HeathB]

If you stop doing the CO2, I'm pretty sure the ph will jump back to what it was and shock the fish. Someone else will have to mention the other stuff.

 

[taylorodw]

The crushed coral will still affect the pH even with a Flourite covering. If you don't want to lose the bacteria, try this.

Fill a container with your old tank water. Remove your filter (the whole HOB, with water still inside it) and submerge it in this new container, at least enough to remove the filter pad while keeping it submerged. If you need to keep the bacteria there for any extended period (more than a few hours) put in some ammonia, fish food or old dirty gravel.

Then empty your tank, pull out the old substrate, and install the new substrate. Repeat the above steps in reverse, keeping the filter pads submerged. Your tank may mini-cycle, but you'll have the right substrate for the pH you're shooting for, and you shouldn't lose your bacteria entirely.