Why only at night?

[Baccus]

I have noticed that some of my red cherry shrimp (even one of the chocolates) go blue over night or get sections of blue. This blue quickly disapears when the tank lights come back on in the morning. I dont use fertisers or even shrimp soils in my tanks so I am wondering is the colour change still pH related, or is it just at night time in the total darkness they feel they dont need to "hold" their normal colouration? I am also guessing too that this mean that all the ones that display this blue colour change, are they carriers of blue gene?

[OzShrimp]

Are you running Co2 by any chance in the tank?

I would dare say they might feel less threatened of a night time so revert to the blue color? 

 

[Baccus]

All my tanks are srictly low tech, so only a filter and airstone that run 24/7.

I thought maybe the threat of predators was what made them change only at night, since I doubt the pH should be changing that much at night, because if the pH was changing a lot I'm pretty sure the shrimp would not be breeding up a storm and thriving.