I'd like to start off by saying Seachem is a very good, very reputable company that contributes a lot to this hobby. This post is not intended to criticize them or say they're a bad company or tell everybody to stop buying their fertilizers. It's purpose is to simply make people aware of what is in the ferts they buy. Everything stated here is based off my own opinion and research of plant nutrient requirements. Seachem, please don't sue me lol So: Plant fertilizers can bring a lot of confusion to the planted tank beginner. So can lighting and CO2, but I think ferts get a little less attention than those two. The reason I am focusing on flourish here is because commonly people recommend it to others willy nilly without considering their tank conditions. Plants need two types of nutrients: macros and micros. Macros are required in higher amounts than micros, hence the names. Macros consist of: Nitrogen (N) Phosphorus (P) Potassium (K) Magnesium Sulphur Calcium Micros consist of: Iron Manganese Chlorine Zinc Copper Boron Cobalt Molybdenum (Others, but in very small amounts, likely already in your tap water) The main problem one could possibly run across with using only flourish and flourish root tabs, and even flourite substrate, is that none contain high amounts of macro nutrients, especially the main three NPK macros (nitrogen, phosphate, and potassium, aka NPK). They have nice amounts of micro nutrients, and if you compare the percentage of macros to micros it'll seem like they are similar. Yes, they are similar, and that is a problem for some because macros are required in much higher amounts than micros. Right off seachem's website: Flourish analysis: Flourish tabs analysis: Flourite analysis: As you can see, flourish has 0.007% nitrogen and 0.01% phosphate, which is virtually nothing compared to what plants can and will take up. It has slightly higher amounts of potassium at 0.37%. Flourish tabs have more of each, though all under 0.3%, but is slow releasing and still does not nearly total to what plants could use. Flourite has no macros except magnesium. Now, seachem does make nitrogen, phosphate, and potassium ferts in higher amounts, all in separate bottles. This can be one way to cover all of your important NPK nutients. Here is seachem's dosing chart for all of their plant products: And in fact, upon emailing Seachem to ask about flourish, the representative told me that flourish is not actually meant to be a complete supplement, but to provide a baseline of nutrients in base levels. They explained that, due to different levels in different aquariums, a fertilizer that is "all in one" could result in difficiencies in one or more nutrient in the NPK ratio (IMO this can easily be avoided with the EI method, see bottom of this post for more info). They added that for proper NPK dosing, they have the separate bottles like I mentioned. NPK dosing is sometimes falsely believed to cause algae. There seems to be the belief that fish will supply all that the plants need, and adding too much nitrate and phosphate will cause algae. A little bit of research into this reveals that this is untrue. If you have a balanced tank, extra ferts (within reason) will not cause algae, which is precisely the reason why there are not algae blooms happening everyday in aquariums that recieve daily ferts in high amounts. It also has to do with the life stages of algae and how different stages require different nutrients. A lot of the time, the reason for algae is not excess nutrients, but too much light, too little CO2, and in fact too little nutrients. Basically, give your plants all they need to outcompete algae and let light be the only limiting factor. If one uses extra ferts via the EI method, a 50% water change at the end of the week is done to "reset" the nutrients and prevent an overload. You can get a little more in depth and analyze the ratio of various nutrients to each other, but giving more than enough to eliminate possibility of deficiency is the gist of it. To do the opposite and limit nitrates and phosphates is harmful. You can never eliminate all the nutrients in a tank. By the time you are able to starve algae of all nutrients, your plants are long gone. See post #3: How specifically does EI method prevent Algae? - The Planted Tank Forum And: Algae and Nutrient Deficiencies - The Planted Tank Forum And also: Diatoms: For the new aquarist and debate thread - The Planted Tank Forum In low light tanks plants do not grow as much, and therefore fish can sometimes supply all that is needed. However, I am still seeing people asking about why their plants have deficencies in their low tech tanks. Unfortunately, most people cannot easily measure how much of the other nutrients are in their water, so we must solely go off nitrogen in this case, and liquid tests aren't extremely accurate either. (API has a phosphate test, whether it is worth it or not is up to you). But deficiency is not hard to spot, if your plants have yellow, brown, or stunted growth, compare your plants to a dificiency chart to see if they are lacking nutrients. Another important consideration when choosing a fertilizer is the growth rate of plants. Light dictates that to a large extent, but even in a low light tank there can be a large range of growth rate. For example, anubias and most hygrophilas are considered low light plants, yet hygrophilas have the ability to grow much faster than anubias. They will need more nutrients. Can you get away with using only flourish in a less than fully stocked or a medium to high light tank? In my opinion, not without the plants eventually developing deficiencies and encountering slow/weak growth. This will widely vary on many other things such as substrate choice and even water hardness, so the key here is knowing what your tank's conditions are and researching the fertilizer that will best suit your plants' needs. For people afraid of poisoning your fish or adding too many "chemicals," there isn't anything to worry about. The compounds we add are just minerals and metals, some of which can be found in low amounts in tap water. You'd have to actively try to overdose most ferts to harm fish, and as far as I know, the only fert that can kill fish is liquid CO2, which is made from an industrial chemical. To sum it up, flourish is an excellent source of micros and has a large variety of nutrients, just not macros in high amounts. It might be enough for you if you have a low tech tank and if you're sure that your fish can cover the rest. If you see macro deficiencies, or your plants are not growing as much as they should be compared to your light and CO2 levels, you might want to consider additional fertilizer as needed. If things are working well with flourish, great, by no means do you need to run out and buy some more ferts. For people who have not yet bought any fertilizer, do lots and lots and lots of research on what exactly you are trying to acheive in your tank and what fertilizer will best help you get there. Read the nutrient analysis of whatever fert you're about to buy so you know what you're getting. As for me, I did buy a bottle of flourish to use in my own tank. I didn't see any difference from when I was going without it and my plants started to show magnesium deficiency. I switched to Nilocg's Thrive, which is designed to be an EI method liquid fert, and also their GH booster to add extra magnesium. Plant growth picked up, and the deficiency went away. Thrive lists an analysis of: N 3%, P 0.8%, K 9.4%, Fe 0.47%, Mg 0.062%, Cu 0.009%, B 0.023%, Co, 0.0002%, Mn 0.06%, Mo 0.0018%, Zn 0.016%. Here the NPKs come in much higher amounts than the micros. You probably don't need this "intense" of a fert in a low tech tank, in moderation it can't hurt though. The issue with ALL liquid fertilizers is you cannot change the composition of the fertilizer to better suit your tank's needs. That's where dry ferts are useful (and much cheaper). However, for the majority of people who are not running aquariums with particular needs, liquid fertilizers will do the job. EI reseach if you're interested: EI dosing by Tom Barr Non CO2 methods by Tom Barr Edit on January 8th, 2018: I've made a short video analysis of some of the common fertilizers on the market, including some mentioned in this post. Hopefully if you're still unsure about what to buy, this will help summarize the nutrient content of each fert.