Shrimp stays near surface walls

[Opaela]

I need some help. My shrimp and shrimplets are staying near the surface of my tank wall quite often lately. I still see some in lower part of the tank but it's much less than ones near the surface.

The bigger ones used to stay on the top of my volcanic rock or down below the rock but they now stop hanging out on the rocks.

five causes I can think of:
1. lack of oxygen ( i turn lights more than 12 hours tho )
2. feeding too much spirulina powder( once per week pretty recently) and they are now used to stay near the surface as it's closest to get food. ( they finish it within a day and go crazy for it)
3. feeding too much spirulina, and the poop contaminates water deep down the tank.( too much for the bacteria to break down?)
4. hair algae growth in other parts of the tank which causes shrimp to hang out elsewhere ( not visible tho)
5. too many shrimp ( now i can roughly count 7 mature shrimp, 10 almost mature shrimp, and 30-60 small shrimplets or more)

My tank is 3 gallon-ish. Also these shrimplets were bred in this tank.( they start off 7ish and now my mature shrimp stops carry egg sack anymore) The reason I fed spirulina powder often recently is because of too many new born shrimplets( the youngest was 3 month ago?). I wanted to give them enough food to grow. And they went crazy for it too.

Any ideas guys?

[Opaela]

I just performed a partial water change and now they are disturbed. Still, a good number of them(all young ones) hanging around the surface.

Now I believe the young ones are just used to chilling near surface since the spirulina powder was on the surface... The fact that I did a water change and they are still near the surface means it's probably not water/oxygen problems.

I will stop feeding them for a few weeks and see if it changes their behavior patterns.

[Dch48]

It is probably because as you said, some of the spirulina stays at the surface so they hang out where the food is. They do love the stuff. I give mine a very small amount every 12-14 days and they get very active when it goes in. I would reduce the feeding.

[sliphorn]

It is probably because as you said, some of the spirulina stays at the surface so they hang out where the food is. They do love the stuff. I give mine a very small amount every 12-14 days and they get very active when it goes in. I would reduce the feeding.

..
Agree. I would stop feeding altogether for quite sometime.
..

[Opaela]

Thanks for the advice. Two more days passed, still no change yet.

[Mustafa]

Judging by how much algae you have growing all over you tank, I'd say that you should just stop feeding instead of reducing. That algae will last many, many months as food, and your shrimp will actually be happier.