When i do my water changes i normally boil the kettle with each bucket,today i did a 50%water change without the kettle the water temp dropped from 26c down to 17c.My tapwater is very cold the o's seem ok with itbut theres a gourami type fish in with them 5 mins after i fin the water change and the temp in the whole tank had dropped to 17c the gourami thing spead round the tank obviously the water had gone too cold for it but the o's seemed ok and still do,there carrying on as normall.ARE THEY OK THOUGH???Any experience or oppinions on the cold water water changing!!!

You should try and avoid sudden large changes in temperature. Unfortunately it does sometimes happen, especially if you're taking the water straight from the tap through a hosepipe.
I've had it happened on more than one occasion, the water suddenly runs cold. Mind you, having a crap boiler doesn't help:lol:

The problem is, if the water does change temperature very quickly, this can put fish under stress. Stressed fish can be more vulnerable to diseases such as White spot and more seriously, hole in the head disease.

A large change in temperature is not a good idea. I have heard that if it goes in too cold they get some problem called gas bubble disease or something like that (someone mentioned it on here). They also get stressed and can as already mentioned get things like HITH.

To avoid this get a mixer tap and a hose adapter and connect a housepipe to the mixer tap. Set the temperature as close to your tank temperature as possible and refill

With a mixer tap though it's hot water from you're system.Water out the hot tap can carry legionares disease if we were to drink it we run the risk of getting this disease,Is it same with the fish,is it safe to use hot water from you're tap???

I have never had a problem with hot water from a tank system, in fact i have only ever heard of people catching legionares disease from commercial hot water systems so something must be different with commerial hot water systems to domestic systems. I am no expert on this so if anyone knows any more on this subject i would like to hear what they have to say

if you need to do a 50% water change rather do a 15% at a time every 2hours or so untill yr tank is back to its normal temp by doing 15% u r not adding to much water at a time and yr heaters wont hv to much hassle getting it warm.

the sudden drop is really terable for yr fish trust me i lost my clown loaches with cold water change added salt to try and stop the stress and killed my loaches.