I use the generic tractor supply brand. I think 2.5 gallons is $59. It works well in my 160 gallon tank.

Did you check your screens before refilling tank? If there was some leftover roundup in the filter housing it will gel up and cause problems. I will empty any leftover mix into 5 gallon buckets, then clear screen and run 15-20 gallons of clean water thru it to make sure no mix is in lines, hoses, pump etc.

Then when I am ready to reuse the saved mix from the buckets i will pour into my tank using a good cotton towel as a filter.