The colombo doesn't contain iron. So to buy a bottle of fertiliser is 9.99. A bottle of iron is 9.99 and a bottle of liquid carbon is 9.99. Seachem do a trio for 13.99. I use the liquid carbon in a low tech tank. I have a lot of of alternanthera rosaefolia that's has really slowed down and Some lower leaves are turning yellow on a few different plants.I don't think you can mix them as it causes something (experts?) to drop out of solution (if that's the right terminology?). I totally get the desire for it to be an easy job to just pump x number of pumps rather than measure out. I have the same approach - having reused pump bottles for the same purpose. Your post is causing me to ask the question though - if the Colombo is working, and the pump on the bottle is working for you to and its the same price - why switch??