question about tempature swings

I have always been told that we should try and maintain constant temp, or raise or lower temp very slow. I am wondering if this holds true with temprate fish. Even in South Alabama in the summer time there is a noticeable difference between top layers of water and the bottom, in almost any river, or large lake.

if i do a 50% water change on a tank and lower the temp by 6 or 7 deg F how is that different than a fish swimming to a deeper location on a river where there is a temp change of the same or different ammount?

I can understand keeping constant temp with tropicals, i would bet the tempature layering in most rivers in brazil or central america is much less than in north america.

O2 content of water is a seperate issue, warm water has less o2 than colder water, but i would think that this can be eliminated using power heads or air stones

Well, fishes in the wild can change their position in the water column at will, so if they get too hot/cold they can always move. Not so in an aquarium. I think temperate fishes should have the same temperature regimen as tropicals WRT short-term changes.

I am a temperature swinger! I change water with cold faucet water year around except for species (few) that I find to be intolerant. I do the changes slow. I Am even a bit lax on acclimating natives. I do it, but likely not as long as reccommended. I find that I have alot more trouble bringing native fish UP in temp, than DOWN in temp. I do not advocate my laziness, but simply say that it causes me no real amount of trouble. To quantify this, ALOT of fish pass through my basement in a year with very little death loss, and many very happy buyers.

What species are you cautious with?

SRBD mostly, seem to be the most susceptible to slimecoat issues of any of the fish I keep. Also various "shiner" types. Other than that Temp swings seem to be a non issue. I am not talking huge temp swings, but less than 10 degrees. Again, I am not advocating this! I am simply stating what seems to work fine for me. I know, I am bad! I break the rules! But a fish that dies from a temp swing, was not healthy in the first place! I believe that it can be used as a tool to cull out the weak.

let me give you a "for instance"

I do 50% water changes on my 40 gal weekly, with a 3year old in the house i have a hard time aging 20 gal of water. In the summer time my tap water is around 86 f my tank stays at 79-80 in the summer. so when i change the water, via python i end up with 83- 84 deg water

the tank is heavily planted and i have co2, the plants pearl constantly (which i have read is a sign of o2 saturation) so i am not worried about o2 depleation, do you think i am causing the fish harm? I add declorinater into the tank about 3 times during the fill up.

thanks

I don't really see a problem there, Harry.

I really would not be concerned. Watch your fish, do they seem stressed? If you are really concerned, keep a couple of ice packs in the freezer, and add them when you do water changes. Should help keep it a bit cooler.

the fish dont seem concerned at the least