Liquid Ferts
Hello Oscar...
The liquids at the chain LFS are like a lot of the stuff there. It's really "hit or miss" and you need to be selective or you waste your money.
I have several large, low tech tanks and the Nutrafin liquid is average in my opinion. Yamato Green has a good product, but you'll need at least 1 watt of light per gallon of tank size for the stuff to work well.
I've just started using very small doses of some liquids called "Earth Juice" that I get from the local hydroponics store. It's all organic and a lot cheaper than ordering on line.
Do your research and you might get lucky and find a good deal.
B