I have a problem with my ambulia that I cant work out.. the top 3rd of them are fine, bubbling CO2 and the very tops are even red (looks really cool) but the growth in the bottom 1/2 starts to go brown after a while and looks very sickly and unsightly.. i dont think it is algae.. it looks liek the bottom is just dieing.. anyone else had this problem ?? Cheers Jon Hammond