@Robin,
First thing we need to understand is what type of tank you keep, or plan to keep? This will most certainly help in guiding you towards the right AF products to meet your needs. Please take the time to download the user guide and products guide to help you learn of the products that AF offers. In the user guide, you will see different types of tanks you can run with AF and products recommended. We are most certainly here to help and guide you, but it is really important to learn about the products and what will best suit your needs. Component 123 is simply a method of replacing minerals, Alk, Ca, and Mg, but also combines the majority of trace minerals and heavy metals that are lost due to coral calcification, of course in fractional parts to that of your basic 3 main minerals. For the biological aspects of AF, many such as myself who keep demanding SPS type corals use the Probiotic Method. This is mainly based on using Probiotic Reef Salt, Pro Bio S(bacteria) and NP Pro(liquid polymer that feeds bacteria/carbon source), to help the user maintain ideal Nitrate and Phosphate levels. Some utilize additional dentrifying bacteria medias like siporax, matrix, and of course soon, AF Life Bio Fil. These medias help with tanks limited with rock and sand, which are far more efficient at harboring these bacteria which ultimately reduce N&P. If you have a high bioload, many fish, or larger corals, you can use AF Zeo Mix, AF Carbon, and AF Phosphate Minus to further reduce nutrients. Each system is different, and each system processes nutrients different, so the recommended dosing can change based on your system. Please take the time to check out the AF guides, and let me know if you have any further questions
Cheers!
http://aquaforest.eu/en/download/