Consider padding of some sort when using the poly tubing with bricks or rebar for weights. You may find after a period of time that there is enough vibration to wear small holes in the poly tubing. We remove poly tubing in ponds every year due to this result. Have had tubing last for as long as 5 years and some as short as 1 year (your results may vary)Originally thought the pulsation from todays piston pumps may cause this more often but had same result from rotary vanes last year also.Self weighted airline as mentioned is available in several sizes and several warranty periods that range from 1 year to lifetime.You can expect to pay approx $1.00 more per ft for premium weighted tubing vs thin wall poly tubing.5/8 ID tubing can weigh as much as 60 lbs per 100 ft section and stays put.