Originally Posted by i heartmypleco
Yeah im reading the back of the bottle now and it says it has all these..
: Potassium, Boron, Calcium,Carbon, Chlorine (why?), Copper, Iron, Magnesium, manganese, molybdenum and cobalt, Nickel, Sulfur, Zinc. (Does not contain nitrogren or phosphorous).
So is this good? and all I have to do now is find a source of phosphorous and nitrogen?
You will have plenty of nitrogen and phosphorus without adding it; that is why it is not included in the fertilizer--which tells me they seem to know their stuff. Nitrogen is found in the aquarium in several forms, namely ammonia, ammonium, nitrite, nitrate and nitrogen gas. The latter is given off during de-nitrification by anaerobic bacteria and will not be sufficient to be an issue, it dissipates into the air at the water surface. Nitrite of course we never want to see, and with plants shouldn't. Nitrate may be present, but with plants will be very low, often zero. That leaves ammonia/ammonium. Ammonia of course is produced by fish during respiration, and during the breakdown of organics by snails and bacteria. In acidic water is changes into ammonium and the plants grab it; in basic water the plants take up the ammonia and change it into ammonium. Plants prefer ammonium as their source of nitrogen, though many will also use nitrate if ammonia/ammonium is not available. So that deals with nitrogen.
Phosphorus is a macro-nutrient for plants and an important one. Plants assimilate phosphorus in the form phosphate via the roots from the substrate [for substrate-rooted plants]. There is more than enough phosphate present in prepared fish foods. It should never be necessary to add this nutrient. Too much in the water column can contribute to algae; in the substrate it is not available to algae.
With the exception of cobalt, all the nutrients you have listed (yes, including chlorine) are those required by plants to photosynthesize, develop roots, or whatever. There are two others, oxygen and hydrogen (water) and as these both occur in plenty in an aquarium, they are not included in fertilizers. Cobalt is not a nutrient required by aquatic plants as far as I know, so I've no idea why it is included; but with all minerals, no fertilizer will contain levels that are problematic so I wouldn't worry over it.
All of these nutrients are required in specific proportions to each other, and a good plant fertilizer will have them so proportioned. So long as you do not overdose, there is no harm to fish, invertebrates or plants.