i did the same with bottle tops way back when.geenhouse tube heater is a handy thing to have on a thermosatat to.£80 ph testers are no doubt very good.but my £4 pen is still working after 4 years.granted i did have to buy £20 of ph4/7,but they are also needed for the £80 pen.
cheap is only cheap if it comes back to bite you.im only seeing common sense applied here.
keep it up.