Need some Advice on Crayfish Keeping

Hi i am keeping 2 yabbies ( If i not wrong, they should be cherax destructor - abit dark blue, but more like black and another one look dirty yellowish) The other one is quite smaller. All 3 are considered small if they are not dwarf crayfish. They are net caught from the upper pierce, not very beautiful looking compared to those COP/ etc brought from petmart.

I put them in a 2ft x 1ft tank, with white coloured small gravel (still abit of cloudy due to the gravel) and put some on bogwood plant and a small moss)

I got 2 gold algae eater in with them to clear the algae and some dirt. All of them are doing fine with no conflicts.

But i have some problem here, i only have 1 big enuff pvc pipe for the bigger one to hide, the 2 have no safe place. I am trying to find black charcoal bamboo tube for them to hide, but couldnt find at the aquarium. I was also looking for small and fast swimmer fish / guppy that can help me clean the water / tank effectively - but not sure what fish to get. Anyone know what to get and where?

Another thing is i am using a internal filter from boyu with the long flter n sponge ( about 15cm long), and not sure is it adequate to clear the tank well. My water level now is slight less than half the tank filled. If i decided to buy a dwarf crayfish, can i put them tgt with the rest of the cherax with enuff hideout?

Thank you! Sorry i am still a beginner at aquarium keeping, but having great interest in learning and gaining passion in it now.