man I had my chaeto in my dt for like 1 month now, but it isnt growing at all and i think its been belting from two tennis ball size to only one tennis ball size. I believe there are two facts. One is my tank maybe too clean, that dont have enough nutrients for chaeto to grow. Two is not enough water movement, Lots of ppl put the chaeto in their refug so there will be lots of water goes through for sure, but if in a dt, you dont have enough flow for every corner therefore, the nutrients cant be deliver to the chaeto.
now, like the guy on top hes setting up with a new tank, which means will have lots of nitrite and stuff, which give lots of food source for micro algae.