There are some misunderstandings here. Calcium is a macro-nutrient, not a micro-nutrient, essential for cell structure. The Seachem
Flourish Comprehensive Supplement and the
Flourish Tabs are low in calcium because most areas have calcium in their water supply. I have zero GH/KH here, and calcium has in the past been insufficient even with just the liquid, but using the tabs as well improved my swords and cleared up the calcium deficiency. I was using Equilibrium to provide the calcium (primariy) but when a marine biologist suggested this was not good for my fish, I switched over to the tabs and found they did the job.
Potassium is, I agree, also a macro-nutrient. However, plants absorb potassium from the water and not from the substrate via roots. Hiscock hypothesizes that potassium in the substrate may increase the availability of ammonium to plant roots.
Copper is a micro-nutrient, and a key part of enzymes that facilitate respiration inplants. Plants absorb copper through their leaves and roots, although humic acids and organics in the substrate often bind with copper and other metals, making them unavailable for uptake by plants. Tap water may contain sufficient copper, but obviously not in very soft water or RO.
Nickel is another micro-nutrient, used by aquatic plants as an ion in extremely tiny amouonts in the production of the enzyme urease which breaks down the nitrogenous compound urea into ammonia. Apparently it is normally present in tap water and excesses or deficiencies should not occur in the majority of aqwuaria.
Sodium is odd, I had not bothered about this previously, but your comment sent me searching and I think it is necessary. The website of the Royal Society of Chemistry has this about sodium (Na):
Sodium is essential to all living things, and humans have known this since prehistoric times. Our bodies contain about 100 grams, but we are constantly losing sodium in different ways so we need to replace it. We can get all the sodium we need from our food, without adding any extra.
I can see that plants being living things are unlikely to be getting sodium unless we add it.
I may get a bottle of the FlorinMulti next time I need a new bottle (may be a while, I just bought a small bottle of FC last week as I was getting low). But if you are asking my advice, I would in honesty say to use the FlorinMulti if you can get it, rather than Flourish Comprehensive. But in the final analysis, either will likely do the job. How's that for being indecisive!
Thanks for all the help.
