Could you recommend a decent complete fertilizer pls, as I've ordered off the internet previously, powders that are made up with r/o, but to be honest I'm not sure of the quality. I need to dose 350ltrs, changing 150ltrs of that weekly, thanks.
Akasha is quite correct about providing nutrients. Most of us are probably fortunate to have relatively few problems with our water, but if you are aware of significant issues like she mentions, it is wise to work around them.
But assuming your water is fairly "normal," it is safer to dose what are termed comprehensive fertilizers. These will have most everything needed, and more importantly the nutrients themselves will be in relative proportion to what the plants need. And this is very important for those like myself, and I assume you Damian, that are not doing high-tech methods (with diffused CO2 and higher light) but more natural or low-tech with moderate light and relying on the naturally-occurring CO2. I'll explain.
Aquatic plants require 17 nutrients; some are termed macro and some micro, roughly because of the level needed. But there has to be a reasonable balance among these. "Excess" means there is much more of that nutrient than what the plants in the aquarium require. Deficiency is the opposite, when there is not enough of a particular nutrient. Generally, plants have no control over how much of a nutrient they assimilate or take up from the water; they tend to store the excess in some cases, but this can sometimes work against them. Experimental studies have shown that when some nutrients are in excess, plants somehow shut down the assimilation of certain other nutrients. This varies depending upon the specific nutrients. As an example, an excess of copper, manganese or zinc will induce an iron deficiency even though iron may be present in suitable quantity. Botanists have worked out the approximate proportion of nutrients, and there are some fertilizer preparations available where this is reflected in the nutrient ingredients; I'll come back to this momentarily.
Nutrients occur naturally in the aquarium if fish are present. Technically, all required nutrients are likely available in prepared fish foods, though there may be a deficiency of a few of them. So allowing organics (fish excrement, dead plant matter) to work its way into the substrate (rather than quickly vacuuming it all out) allows the bacteria in the substrate to break it down. This produces nutrients that the plants can them take up through their roots in the substrate. However, some nutrients can only be taken up via the leaves, so these nutrients have to get into the water column. Another source of nutrients, here the "hard" minerals like calcium, magnesium, and a few others, enter the aquarium with water changes. These "hard" nutrients are usually minimal in prepared fertilizers because most people haver sufficient in their tap water. This is why I always ask about the GH (general hardness) of the source water; in my own case, I have extremely soft water, and I need to supplement the hard minerals beyond what are available in most fertilizers.
The GH of the tap water and the fish load and feedings thus provide plant nutrients and in some cases may be all you need. Different plants have different levels of need, so slow growing plants need fewer nutrients (and less light to balance), whereas fast growing plants require more of both.
The first place to start with adding nutrients via fertilizers is with a comprehensive liquid supplement. This provides all nutrients to all plants, be they floating, rooted in the substrate, etc., because the water circulates through the substrate and all plants can take up the nutrients via their leaves and roots. An excess of nutrients, beyond what the plants in the aquarium require, usually leads to algae problems; and similarly a deficiency can do the same because algae is not so fussy as higher plants. Same with the light if it is not balanced.
And at this point I must mention carbon, which most plants take up as CO2 (some can also use bicarbonates which are greater in harder water, though plants tend to prefer CO2 first). CO2 is produced mainly by the breakdown of organics in the substrate; this CO2 is much greater than what the bacteria, plants and fish will produce via respiration. As we rely on the natural CO2, and can add all of the others, we have to find the balance. Overdosing fertilizers beyond the available CO2 will lead to algae; everything always come back to a balance. CO2 is highest after the night, or period of total darkness, because plants are not taking it up because they don't photosynthesize without sufficient light. Once the tank lights are on and photosynthesis can begin, this CO2 is taken up by the plants. At some point it will likely be used up, and photosynthesis slows and may even stop. Any light and other nutrients then will only feed algae. This is why we fiddle with duration sometimes, if the intensity and nutrients seem OK, duration is how we gage the CO2 situation.
I use Seachem's
Flourish Comprehensive Supplement for the Planted Aquarium. It has all nutrients required (except oxygen, carbon and hydrogen) and in proportion, though the "hard" minerals are limited since as I explained above there is normally sufficient of these in aquaria; similarly, nitrogen as ammonium and nitrate is limited because with fish one usually has all you need of this. Another product that is identical for our purposes is Brightwell Aquatics'
FlorinMulti. Either of these will likely be all you need. They are concentrated, so it takes very little to do the job. I use 1/2 teaspoon of Flourish Comp per 30 gallons of water, once a week; sometimes twice a week in certain tanks. Again, every aquarium can be a bit different depending upon the biology so experimentation may be necessary. There may well be other brands that are like these, but I know these two do the job.
Heavy feeding plants like large Amazon swords, Aponogeton, lilies may benefit from additional nutrients added to the substrate. I use Flourish Tabs for these plants which I have in three tanks; the other tanks with less demanding plants manage with just the liquid.
Hope this helps, but don't hesitate to ask further. And thank you for your kind words, which are much appreciated.
Byron.
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