i dun open fish shop la...@@

personal shop ada la..hahahaha

sometimes when water cloudy means fish spawning le..dun play play..
usually early in the morning.

water unusual cloudy...hehehehe

tetra is wad fish lai de ?

With or without gravel, I dont think is an issue here. But if you wash your filter media too clean...That's an Issue!  

Did you 'cycle' your tank before adding the fishes?

i usually just throw away the old wool...replace with new ones

Actually, you could still use the wool as long as you wash it in the tank water when u are changing the tank water. For an example, when u are drawing out the water from the tank in a pail, just wash the filtering media in the pail then replace it back. This is important because you dont want to kill all the good bacteria when you are washing it thru the pipe water which cointain chlorine.

Change the wool, if the filtering capacity is too low or because it is too dirty. For me, i usually put 3 layers of wool in my top filter. I will only change or wash a piece each time when i change water which is once a week. I wont change all the filter because the good bacteria needs time to cycle.

Cheers.