Moving and only rainwater accessible.

[Colin_T]

Settled on this. Sounded like what you described with the finger nail size. Hope they will do the trick

those white shells look like the ones I used

 

[Johnykiwi]

those white shells look like the ones I used

So I just wash it an chuck it in the tank?

 

[Colin_T]

So I just wash it an chuck it in the tank?

Pretty much. I found the best way to rinse them is put some in a course fish net or sieve, then use a garden hose to spray water on and through them. It will wash out any fine dust (calcium) and the dust won't end up in the tank.

If you don't have a net or sieve, put some in a bucket and squirt it with a hose, then tip the water out and hose again. Continue hosing and tipping the water out until the water is clear.

*NB* Stand upwind when pouring the shell out of the bag because there will be a lot of dust in with it.

*NB* The shell can cut fish net so use an old net or a sieve.

When the shell is clean, put some in a bag or compartment in the filter if you are adding it to a filter. Or just spread it over the base of the tank, but it doesn't look that nice when mixed with gravel so try to put it in a mesh bag somewhere.