First, stats:
Tank
Planted 40g breeder estblished early October 2021 (first fish added mid-November)
Located in my office where I sit at my desk about 6 feet from it all day long most days. Room is usually pretty quiet.
pool filter sand substrate layered on top of some aquasoil and gravel
Oase BioMaster Thermo 250 (I know it's overkill)
NICREW SkyLED Plus Aquarium Light
Stock:
7 corydora punctatus
2 otocinclus (bought 4, two died)
12 leopard danios
4 cherry shrimp
lots of plants
Tank parameters:
75F
pH 7
0 ammonia
0 nitrites
~25 nitrates (usually between 20-50)
Weekly ~30-40% water changes
Currently fighting off a bit of an algae issue
Feeding
daily pinch of xtreme krill flakes for the danios and sinking pellets for the cories
occasionally frozen brine shrimp or frozen blood worms
Hello! Looking to get some help on my first real aquarium. I did research for months before buying anything and ran with only plants for weeks before buying fish, making sure my cycle was established.
The Problem
My problem is the cories which I bought 8 of back in November (have lost 1 since). The reason I got them is because I thought they'd be active and fun to watch. The first week or so I got them, they did what I would have expected, hanging around together, glass surfing every once in a while. But within a month they became very very shy and have remained that way.
They stay in the back behind the rocks and among the plants all day long until it is completely dark. I mean the sun is set, the aquarium light is off, and all of the lights in the room are off. If I come into the dark room with a dim light to try to check on them, they may hang around for a few seconds, but most of them will quickly dart to the back and hide. In addition to that, they're terrified of me. If I'm at all close to the tank and looking in, sometimes I'll see one that's in the back dart away to somewhere more hidden. And sometimes when I do a water change, if I do anything to scare them, sometimes one of them will completely freak out and swim for their life all over the tank.
Things I've tried, with seemingly no effect:
I had hoped adding the danios would help them gain confidence, but it did not
dimming the aquarium light or leaving it off during the day
changing to a horizontal spray bar
changing to a vertical spray bar
lowering the flow
raising the flow
feeding them at different times of the day and in different places in the tank
Is there anything else I can do? I was really excited to get what I thought were going to be really active, fun fish, so it's disappointing that I hardly see them. In addition I'm worried that this behavior is because there's something about the tank that isn't good for them.