How do you Lower Water Hardness In a fish tank?

I just bought a test kit, even so I owned fish for a year ( even though I just found out about the nitrogen cycle..). Anyways, I found that I have no ammonia problems, but that I have a high pH, and High water hardness (380-420). And my fish are taking an abnormally large amount of craps. I'm not sure what my fish species are, but I also found that there are now baby minnows in the tank, so some of the fish must of mated =). Any advice on how to lower the water hardness and possibly any side comments on what to do with the baby minnows? Oh, and none of the fish are big enough to eat them (hopefully). I keep fresh water fish.
Answers:
Unless you have species that absolutely require soft water (like discus) or low pH, I wouldn't worry about changing either - and it's probably the hardness that's causing a higher pH. Most fish are at home in pH levels from 6-8, and I've kept tropicals at a pH of 8.2 with no problems.

About the only ways to do this would so the pH doesn't fluctuate would be to use a water softener at your home, or use reverse osmosis water (you can buy a filter for your home or get it at larger supermarkets bottled or from self-serve dispensers). You could mix purchased water with your own in whatever ratio necessary. Chemical buffers cause the pH to swing, and the fish prever a stable environment.

Your fish also seem to be suffering from constipation. This could be from being fed too much (only give them what they and eat in 2-3 minutes twice a day!), too much dry food (soak flakes or pellets a few minutes before feeding), or incorrect foods (if you fish are herbivores or omnivores, they'll benefit from getting some vegetable matter in their diet). Try not feeding them for two days, then give them some cooked peas with the skins off. This will help with extra fiber to "push" anything else throught their system. After that, feed a little less than usual, and try adding a bit more variety to what you feed - fish will also eat squash, romaine lettuce, algae flakes, and other veggies if their frozen so they soften. The babies will probably eat what the adults do - you may just need to crush up the pellets/flakes so they're a smaller size.

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Find out what pH level your fish prefer...you can search on google, and then you can buy a chemical to either lower the pH...don;t lower by more than .2 every 24 hours or you can kill them, or they sell perfect pH. Buy the one that matches the pH they prefer and add it every time you change the water. Easy as can be!