if I have an 18 gallon tub. does it matter the size of the air pump? or how many ? thanks or does it matter where its placed or just that its constantly running with an air stone
the more bubbles the better... so go as large as you want.... I have never read someone wanting the minimum... and the air stone has to be on all the time.. but make sure its at the bottom of the res... some float... use aquarium silicone to hold it to the tub if you have to... good luck
it matters where you put it also if its just a little air stone. I had a little blue air stone in a bubble bucket and the roots were much longer on the side with more bubbles.
for your 18 gal tub I would be tempted to go with a boss hog micro-pore stone and pair that up w/ an 80w pump. It is similar in concept to SH's oxyponics kit setup but higher octane. If you have a strict budget requirement then you can safely ignore everything I wrote before.
no, you'll be fine. You'll just need to keep an eye on the res temp and make sure the air stone diffuses enough oxygen. More aeration is usually preferable but there is a diminishing return at some point. Also, with cheaper stones you may want to tie them down since they tend to move around w/ the water current.