I am curently using silica sand in the filter and honestly had not
thought of using different sand.

After having the sand filter on and off for five days it has now been
operative continuously for 24 hours and (touchwood) no signs of the
dreaded ammonia.

I did add four new fish last weekend but as they are only 6 inches
long compared to the five existing fish of 24 inches plus I do not
expect the loading on the filter to rise much.

I will post any changes as soon as.

Carl