Why are my fish acting weird post water change?

Ok need some expert advice. Just did a water change in my 20 gal tank. All parameters appear to be good API test kit, ammonia 0ppm ph 7.6 nitrite 0ppm nitrate 5. But now all my tetras and my guppy are hanging at the top of the tank. They seem calm, not gasping for air, some are chasing each other so not lethargic but still kinda different behavior than I am used to from them. We have two sponge filters and a bubble wall so plenty of aeration. What am I missing or am I just overreacting? Also, have some mystery snails that just floating at the top but they are alive and have been active off and on between floats. Tank has been a struggle to cycle but has finally seemed to be regulating in the last week with daily checks and weekly water changes that vary based on parameters between 25-50%.

 

Was the temperature consistent?

 

Was the temperature consistent?

It went down a bit but now it’s back up it stays between 76-78 and dipped to between 74-76, but it’s back to normal now.

 

did you forget to dechlorinate the water you put into the tank?

 

It went down a bit but now it’s back up it stays between 76-78 and dipped to between 74-76, but it’s back to normal now.

Why did it go down a bit? The new water temp should match the tank water. Or pretty close.

 

How often do you do water changes. My fish are always more active when i change the water. Also colder water when doing water changes is supposed to simulate rain and encourage spawning in some fish

 

did you forget to dechlorinate the water you put into the tank?

No I added prime and added stress coat when they were acting so weird. They seem to be returning back to normal. I think maybe was combo of stress and the temp change

How often do you do water changes. My fish are always more active when i change the water. Also colder water when doing water changes is supposed to simulate rain and encourage spawning in some fish

we have been doing it every week as we were trying to get the parameters right, now that they is stabilizing hoping to move to every week and half to two weeks. We have also encountered a lot of algae in this tank all of a sudden, but the culprit is a large window. I have taken to putting shades around the tank during the day (like the ones you put in car windows to shade a baby in the car). To try to cut down on the amount of sun feeding the algae during the day.

 

Well, here’s a quick update, things aren’t looking good. All the Tetras seemed to have returned to normal, but last night my Molly started acting lethargic and drunk, not swimming so much wonky like swim bladder disease, just sort of bobbing in the water with the current and barley moving her front fins and not moving her tail fin at all, and kinda running into decorations and the walls of the aquarium. Some research and other searches suggested it may be caused by OD of water conditioner during the water change that deoxygenated the water too much. So I immediately did another 50% water change. The guppy who was also acting irregular by this point immediately improved and was acting normal, however, the Molly’s condition has worsened she is now laying at the bottom of the tank, hardly any movement but she was breathing when I left this morning and the guppy was also back to odd behavior, he was floating at the top, only barley moving his side fins but not his back fins at all. All other fish seem to be ok, acting completely normal and snails are no longer floating they all seem to be fine. I am very upset and am pretty sure both the Molly and Guppy are probably not going to be alive when I get home or survive the day. These two are some of my favorite fish and I am feeling like an utter failure . I just don’t know what went wrong and I’m trying so hard to do everything right. Last thing I want is to cause harm or suffering in any way to my fish, snails etc. I am very depressed and so defeated.