Fish breathing heavy

Hi.
I'm having problems with my tanks. Every sunday I do my water changes and then I check my fish breathing heavy after it. My water stands for about a day with prime.

my filter returns are above the water on both tanks and just seem like it is not helping.


my co2 is the same as always. I do NOTHING different. It id ONLY after water changes.

 

Temperature difference maybe?

 

i wood recon that the co2 wood maby be 2 high ? temp would make the fish go to the bottom the only reason they would be on top is to get air

 

While the water is standing with the prime for your water changes why don't you put in an airstone so that the oxygen is not depleted while the water stands. that should solve your problem. Maybe just an hour or 2 just before your water change you can add the airstone

 

Thanx for all the advice.
Can't be co2 as my co2 levels are exactly the same as always i even adjusted it down a bit to be safe.

Ok so what i did now is i went and got 2 more timers (one for each tank) and i added air pumps with airstones that only go on once my lights and co2 is off.

Only thing that is bothering me is that it is in both tanks exactly the same.

 

There is a O2 test kit available from Sera, not sure how accurate or sensitive it is, but may be interesting to test both tanks and see if it registered a difference in O2 levels. I have used on my one tanks, also CO2 infused and have tested the water when fish are gasping, happened mid summer during very hot days, and it does show low O2 levels. Turning off the CO2 and adding air stones to the tank reverses the situation within 15mins.
I'm also not sure how accurate CO2 indicators are. What I do know is, that at the margin, things go south very rapidly if the O2 levels drop only slightly.

 

it is weird that its in bought thanks that it happins ...