Garden hoses have a softening agent built into them to stop them kinking. More expensive garden hoses that don't kink, have more of the chemical than cheaper hoses that do kink. They release the softening agent in warm or hot weather and it is poisonous to all animals, birds and fish.
If you want to use a garden hose to fill an aquarium, use the hose to water the garden for 5 minutes to flush out any of the chemical, then fill the water containers.
Black poly pipe (irrigation tubing) does not have the softening agent in and can be used instead of garden hose. However, some cheap poly pipe can contain lead so again, flush the hose out for a few minutes with running water before using it to fill tanks/ water holding containers.
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Why does everyone with big tanks have issues about doing water changes. Make a home made gravel cleaner.
Get a 1, 1.5 or 2 litre plastic drink bottle.
Cut the bottom off the bottle and throw the bottom bit away.
Remove the cap and plastic ring from the top of the bottle and throw those 2 bits away.
Put a garden hose in the top of the bottle and run the hose out the door onto the lawn.
Gravel clean the tank and drain the water onto the lawn.
Remove the bottle and use the hose to water the lawn/ garden for a couple of minutes before using the hose to fill up a couple of big plastic storage containers with water.
Add dechlorinator to the new water and aerate for at least 5 (preferably 30) minutes.
It's preferable to make the new water up before doing the water change so it can aerate and mix while you are cleaning the tank. Then just fill the tank after it's been drained.
Use a small water pump like an AquaClear 802 or similar and a length of hose to pump the dechlorinated water into the tank.
Make a U out of pvc pipe and put it on the outlet of the hose from the water pump. The U hangs over the side of the tank and lets you wander around while the tank fills up.
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I used to gravel clean and water change over 100 tanks a day using a 2 litre plastic Coke bottle gravel cleaner with a length of clear hose. Minimal mess, no buckets, no spilt water, just get in, gravel clean and drain, and refill. All done.