Rock hard water stocking questions

Cichlids

Go with African cichlids. For a 30 gallon, 5 would be the max you could put in there since they grow to 4 or 5 inches. A good mix of color would be an electric yellow, a couple of striped zebras and snow white socolofi would look nice. Forget about live plants with those fish, though...they will tear them out and eat them. They are diggers and omnivores, so plastic plants with a heavy rock holding them down will be the best choice. Give them some torn up pieces of romaine lettuce or raw spinach to munch on 2 or 3 days a week in addition to whatever fish food you give them and they'll be happy.

Cichlids would be happiest in the tank, but it doesn't necessarily mean you can't keep other species. We have tetras and gouramis and guppies in our hard water (pH 8.5, kH 260ppm, gH 400ppm) and they seem to do okay. I mainly say this as a 30g is a little on the small side for a cichlid tank, but a good size for other smaller species...

IMHO a lot of species will acclimitize to the water conditions. Neons seem to have the most trouble, but then I think neons today are somewhat overbred and probably 'weaker' than they should be. Australian rainbows handle a wide range of water and the Australian gudgeons will live in anything I think. I just found a colony of about 6 of them, one about 6 inches long, living in our water tank. Must have been there for years. Hard to tell how many as the tank is 6000 gallons and very dark. The purple spotted gudgeon and northern trout gudgeon are a nice looking fish and very interesting personality wise but you don't see them overseas that often. Guppies handle the hard water well, though it seems that the fry that are born in the hard water do better than ones that are bought in... Haven't had gourami in hard water very long, but they are doing okay so far. Bloodfin and glowlight tetras seem to do fine.

You can also dilute the hard water somewhat by adding RO water to the tank... We don't really do that here, but we have a difficult situation in that we have really hard water most of the year, and then totally soft rainwater for about 3 or 4 months... At the moment we only have rainwater on tap, so I have to go get hard water pumped to mix with the water change... Bit of a pain.

Stocking Q

Theres also Tanganyikans. They require more territory than malawis but 30 gals would make a great shelldweller tank, great personalities.

We keep a lot of fish in our hard, pH = 7.8 water: a variety of tetras, angels, rasboras and of course, african cichlids. Stability of water parameters seems to be more essential than matching identically the 'native' waters. Also, a 30 gallon is too small for most Malawi cichlids. For example, I'd disagree with the above recommendation regarding zebras. They are not appropriate for such a small tank, IMO, unless they're small juveniles. Yellow labs may be OK, though, in a group of 4-6. Add a trio of a small catfish (e.g., Synodontis petricola) and you'd have a nice tank.

HTH,
Jim