My bulbs are the square ones. There are two of them in the hood of the unit. Honestly, getting them started was the hardest part. After they were about a month old, my time into them declined drastically. I was checking them about 5-10 times per day in the beginning and it dropped off to about 1-5 after that, and now I am down to opening it up to get a little extra fresh air inside and to just look at how far I have come. I hope yours works out well! I didn't have any sponges so I went with a rockwool cube that was just laying around. Cut that down and pushed it into the opening and everything worked out fine. PH could have been your problem.