an open resevoir is not a good idea. you will need to put basket cover on the bucket or something similar to lightproof it. if light goes in the res. it will cause huge problems such as algae growth and no o2 for the mj becuase the algae consumes it all 1st. also this will reak havok on your ph. if you are not an experienced grower i would suggest just putting the cubes in a pot of soil, or soilless such as promix. if you are an experienced grower then do a little more reasearch on dwc hydro and then build your bubbler. good luck