Make sure you flush water through any garden hose for 5 minutes before using it to collect water for fish or drinking purposes.
Garden hoses have a softening agent in them and it is extremely toxic to all animals, birds, fish and reptiles. The softening agent helps stop the hose form kinking. The warmer the hose, the more softening agent it leaches into the water. Flushing water through the hose for a few minutes helps to remove any softening agent and gives you cleaner safer water.
Black poly pipe (irrigation tube/ hose) is hard and not flexible and does not contain softening agents. Again though it's a good idea to flush them for a minute or two before collecting water out of them.
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In some countries (not sure about the UK), you can buy bags of fine gravel and sand from mineral companies. In Perth where I am, there is a company called Cook Industrial Minerals and they used to sell to anyone that wants to buy the stuff. The website says they don't anymore
It's where a lot of pet shops buy gravel and sand from, and then re-bag it at the shop. You can get it from them for 1/4 the price most shops sell it for.
You might have something like this or a landscape supplier that you can buy small quantities from.
COOK INDUSTRIAL MINERALS Main Yard (08) 9417 1111
[email protected] 28 Cutler RoadJandakot WA 6164 Monday to Friday: 7.30am – 4.00pm White Silica Sands -0.300mm, -0.425mm, -0.500mm, superfine, foundry sand, supercut and -1 + 0.500mm and FRAC sand on request. Lime Lime sand, Lime sand oversize...
cimonline.com.au