I unfortunately can't take them home since my 20 is stock full of guppies and guppy babies. I don't think there is room for them there. I will look into increasing the pH with the shells as mentioned above.
The downside is that the other fish WANT the softer water, lower pH. It's a damned if you do, damned if you don't sort of situation.
PS - BTW, as an FYI, if your pH is at 6, your tank isn't showing nitrates because your filter bacteria are either starving or not there. You can't MAKE nitrates at 6.0
When the pH is that low, the ammonia produced by the tank is actually ammonium. The ammonia converting bacteria (that convert to nitrite) can't process that.
As such, if you go and raise the pH right now, you'll likely kill or hurt your fish since it'll be a situation where you have no filter bacteria. You'd be highly advised to treat this like a fish-in cycle situation, or go and get a precycled filter from your other tank etc.
At very low pH ammonium acts like nitrate at high pH...it's only harmful in high concentrations.
At 6, there is no cycle...the bacteria can't operate that low, and will starve off or not grow. You handle ammonium build up with water changes and plants.
PPS - that's why you generally want your pH above 6.4 at all times, to keep filters working. Keep it below 6 and understand the risks and benefits, or above 6.4 at all times.