I think he was asking what it would be used for mean.... as a quick filter foir the tank, or used on UGF...... or maybe you just want to us it to make a current or waves.... Either or I like aquaclear power heads, never hae had a problem heck I never had on breakdown yet. As far as flow rate for aquaclear is go as such:
10 - 80gph
20 - 125gph
30 - 175gph
50 - 275gph with rev flow,,,,125gph
70 - 400gph " " " 175gph
901 - 935gph
for a 55gal tank a aquaclear 50 is recommended.
As far as your sub. for plants..... I using eco complete in 2 tanks a 55 and 70 gal tanks..... very happy with the results, but after 18 months you are back to adding ferts as with any plant sub.. It may not be worth the investment. If you discide to just use gravel 3mm gravel is best for plants. then you just add fert tabs to each plant (usually good for 3 months) and weekly liquid ferts... and you will get the same effect.