120g low tech/light question
So I recently have added plants to my 120g established tank, low light style. I only have one t8 zoo-med flora sun bulb and an (18 x 1w) LED strip at 6500k. The plants are all doing great, but I have a small outbreak of diatoms, and was wondering if it could be at all light related, and not just silica leaching, since the tank has been going for 3 years with only plants added.
The plants are: Anubias (lots of it), bolbitis, crypt wendtii, brazilian pennywort, spiral vallisneria, elodea densa, amazon sword, and some HUGE (tall) unknown crypt.
I do a weekly w/c of 25-30%, temp is 78 F, ph is 7.2, kh is a weak 3, and n03 is 0ppm. That's all I tested for so far, I'm not sure what else to be concerned with.
The fish are all fine, as always, the tank houses 4 large angelfish and about 16 red and black phantom tetras. And 4 nerite snails.
I was just wondering why I was getting this brown algae. I know it's common with new tanks, but this is not a new tank, just newly planted tank. I read in another thread that someone suggested starting with a 6h photoperiod, then bumping up? I might have gone wrong here, idk, I have them on for 9 hours.
Should I cut the photoperiod to 6 hours?