Aquatic fertilisers

 

 

Fertilizers.

Some basics of plant growth and nutrition. Before you make decisions about fertilizing your plants or diffusing CO2 in your tank, please check out Dave Huebert's sensible article:

"Water Plants 101: a basic introduction to the physiology and ecology of aquatic plants."

It's a very brief and sound introduction to plants and carbon dioxide, and mineral nutrients. Dave Huebert offers a counterbalance to CO2 faddism, and anxieties raised by questions of "full-spectrum" lighting and achieving photosynthetic saturation. Once again, it's at Bruce Hallman's page.

Chuck Gadd's "Introduction to fertilizers" is the clearest brief primary orientation I've seen.

Jim Kelly pulled together some sensible, well-explained summaries of plant-growing basics in two articles. One is "Great aquarium plants, real cheap," at:

http://www.hallman.org/kelly.html

The other is "How to grow beautiful aquarium plants on a student budget," at:

http://www.thekrib.com/Plants/kelly-intro.html

Go there, and at least skim over the headings that Jim offers, to get the lay of the land. Then come back here.

About fertilizer.

You can't make plants grow with fertilizer. They have to be growing strongly already. Once they are genuinely growing, you will want to replace nutrients before any become exhausted.

First of all, there are some things not to worry about at an initial stage: don't worry yet about nutrient levels. Some people peering into their aquaria worry about nutrient "levels." What are appropriate levels for all the nutrients in there, they want to know; are any essential nutrients missing? Generally, a good level for all nutrients is a detectable level. If your sensitive test kit can detect any iron at all, for example, it's enough for today. Don't worry about tomorrow. First of all, vascular plants take up more iron - and other micronutrients - than they can use and store them for future need. Algae can't do this. This advantage "higher" plants have is a major tactic you'll exploit in your battle against algae.

And second, the micronutrients are mostly toxic at enriched levels. No one ever poisoned their tank by not fertilizing. So if your tank has just been set up, or if you've only just added plants to it, hold back with the fertilizers. First give your plants some time to get settled in and start putting on new growth. When plants put on new growth in the first couple of weeks in your aquarium, they aren't pulling nutrients from the water or substrate, so much as using nutrients previously stored in their tissues. Karen Randall has compared this process with onions sprouting in the crisper drawer. So, you don't even have to wonder about fertilizers for the first six weeks. Adequate light will do.

There is no one absolute, parts-per-million concentration that will encourage plants and discourage algae. Phytoplankton-laden "green water" conditions can be just as stable as clear water conditions, over a wide range of values. Ratios among fertilizers may be more important than absolute amounts. N is one pivotal ratio, often recommended to be kept at 4:1, four parts nitrogen to one part phosphate. And if Ca:Mg ratios are too low, magnesium may compete with calcium for uptake, and plants may show symptoms associated with calcium deficiency. Low ratios of calcium to potassium may have similar results.

Besides, it takes a skilled eye to recognize the symptoms caused by a deficient nutrient in each kind of plant and to distinguish them from the sometimes similar symptoms of stress caused by competition between nutrients or by toxic levels of the same nutrients. Chuck Gadd posts a chart of symptoms of nutrient deficiencies, expanded from one posted by Neil Frank to the Aquatic-Plants Digest, that is a case in point. Some symptoms are said to appear in mature growth. When symptoms appear in mature leaves instead of new growth, I turn skeptical. Can you be sure you're not seeing symptoms of fertilizer toxicity instead?And if you're assessing symptoms, you'd better take into account the competition between some micronutrients for assimilation and the mutual dependence of other micronutrients. Potentially toxic micronutrients include manganese, copper, even iron. The trace elements, such as boron, have an even narrower range between deficiency and toxicity.

All the micronutrients and trace elements can be expected to be in organic residues, where the mineral elements are incrementally freed and made available, as the chelating organic structures break down. Organic remains provide the best slow and steady release of nutrients, I feel.

The ultimate source of these organic residues? Remember plant guru Diana Walstad's core message in Ecology of the Planted Aquarium: "Fishfood is the perfect fertilizer, whether it's live, frozen, freeze-dried or processed into flakes or sinking wafers, because it is composed of organisms or their processed remains."

When you do come to add fertilizer, add about one-third the amount that the label suggests. Watch and wait. You can cautiously increase the dosage next time. As you can tell, I'm not selling fertilizer.

In general, I'd advise you to add the fertilizer to the make-up water. This is a really useful suggestion. Don't add the nutrients directly into the aquarium until you're very confident that you can judge how much fertilizer is needed, merely by the look of the plants. In the meanwhile, if you add fertilizer to the make-up water instead, you won't inadvertently build up toxic levels of some micronutrients by adding fertilizer faster than your particular plants in that particular aquarium are using them. Catch my drift? If you have a minimal level of fertilizer in the make-up water, why, you're still free to survey all your aquaria, to judge whether additional fertilizer levels should be adjusted. Another benefit of adding fertilizer to the make-up water is that if you find that you're suffering from fertilizer anxiety, you can get relief by doing water changes! How excellent! It isn't unusual at all to see aquarists whose algae have got seriously out of hand and who have posted an urgent cry for help at an aquarium web board, who don't even think to mention that they haven't begun their anti-algae counterattack by stopping fertilizing. Others use three different fertilisers weekly, to be sure they aren't missing that one trace element, yet they add the full dosage recommended by the manufacturers for each one!
Among the macronutrients, carbon is normally derived by plants from carbon dioxide. In water of higher pH values, CO2 is increasingly locked up as carbonate. CO2 diffusion is designed to supplement carbon in the form most easily available to plants. Nitrogen, in the form of ammonia (NH3), and phosphate are continually added to the system by fish metabolism and the fish meal in flake feed. If your plants were ever starved for nitrogen and phosphate, you could add more fish. "Tropical fish! the amusing plant fertilizer." Fish also supplement the system's carbon dioxide.

Besides carbon, the only other macronutrient that is likely to be in short supply in your aquarium is potassium. Though nitrogen is being pumped into the system from ammonia, day and night, there is no comparable source for potassium, which enters only through live, freeze-dried or flake foods. So though terrestrial plants, and doubtless aquatic plants too, may use N and K in a ratio of 1:1.43, it doesn't follow that there is a nutrient deficit that needs to be met in that same ratio.

Every system has an ideal K level. It's not a fixed figure, it's a ratio of Ca:K. Below some range of values for calcium, if you reduce the ratio by adding K in any system, you're likely to see perplexing effects of Ca deficiency. In Ca-rich waters of Florida or New Mexico, you can pretty much add K ad lib. Calcium is so plentiful you could never unbalance the ratio. However, in Ca-poor waters-- such as mine, you can easily upset the Ca:K ratio.

I dose make-up water with potassium so that the plants will use up the nitrogen the systemalready has. For several years I dosed with potassium sulfate in plain old Tetra FloraPride. I like this fertilizer because it has no nitrogen and no phosphate. The potassium sulfate content of FloraPride is 3%, signalled by the nitrogen-phosphate-potassium (NPK) rating of 0-0-3. Phosphate is always the middle number in the N-P-K rating (it's alphabetical), and the two zeros signal "No Nitrogen/No Phosphate." So the rating is 0 (Nitrate) -0(Phosphorus) -3(Potash). That's a good rating. Phosphates aren't even in laundry detergent any more, but aquarists mysteriously burdened with algae problems sometimes turn out to have been adding pinches of sodium phosphate to lower their pH. There's no nitrate either in FloraPride, of course; that would be the first number in the N-P-K rating. FloraPride also contains some iron. But recently several companies have marketed potassium-based fertilizer without any iron.

Recently I've started very lightly dosing my makeup water instead with potassium chloride in the form of a dietary salt substitute, "Nu-Salt." This eliminates the iron in Flora-Pride.

You'll find other not-too-costly fertilizers that are potassium-based. Root-Tabs (Aquarium Pharmaceuticals), for instance. They are also 0-0-3, with some magnesium, iron and sulfate. I push half a tablet well into the substrate next to crowns of Amazon Swords or well-established Cryptocorynes. But I don't repeat until new leaf growth has slowed again.

In my very soft water, plants can exhaust the small amounts of available calcium. I recognize the effects of calcium deficiency when new growth is deformed. Java Fern fronds may be contorted to one side of the central rib, and leaf edges may be pinched or scalloped. A teaspoonful of crushed coral (aragonite: the usual marine aquarium substrate), scattered over the substrate, may do the trick, or in a 10-gallon tank, a single "escargot" snail shell could be all that's required, in my case.

Micronutrients are required by plants in the merest traces.Before you spend money for a designer fertilizer, ask your local water company for a recent analysis, which they will be glad to mail you. Check and see if there's a missing element in your water. ("Got selenium?" It's on the far edge of a possibility, but it's not very likely. Don't pay good money for trendy additives like vitamins, which belong in food, not in the water, where fish can't take them up.

Among the micronutrients, the two that aquatic plant growers seem most concerned with are copper and iron.

Plants don't need copper to build their structure, just the merest trace, which they use as part of some of their enzymes. Those ions are used over and over as catalysts, so they are not rapidly used up. My hunch is that your water is unlikely to be so utterly depleted in copper that any supplement is needed for the plants' benefit. This is not the majority view, however. If your pH is over 7.0, much of your system's copper is precipitated in insoluble forms that are unavailable to organisms-- until your pH drops, through bio-acidification or for whatever reason, and soluble ionic copper is released. Since copper sulfate is sometimes used as a medication, you'll find more about the chemistry of copper in the Treatments folder.

Seachem's Flourish Excel. Seachem aver that their Flourish Excel provides "a simple source of readily-available organic carbon" that is a "photosynthetic intermediate" with iron-reducing properties that promote the ferrous Fe(II) form of iron, rather than the virtually unavailable Fe(III). In this aspect Excel seems to be chelating the iron like a humic substance, is it not?

The named ingredient is "polycycloglutaracetal," which isn't mentioned anywhere on the web except as this ingredient in Excel. (Sure I checked.) Seachem describes the ingredients as "relatively simple organic compounds" such as "photosynthetic intermediates." Scott Hieber started a series of posts to the Aquatic-Plants Digest, 12 June 2002 etc., inquiring how this ingredient differed from simple sugars such as glucose or sucrose, and "Nestor" explained it this way (in part): "The base compound is the acetal, which is formed by adding alcohol molecules to aldehyde molecules. Glutaric aldehydes in general are used for disinfectants. They are also used interchangeably with plant tannic extracts to cure gelatins for specialized applications. Glutarals are carbon-hydrogen-oxygen compounds - C5H8O2 is the dialdehyde." and the next day he went on to add: "I would imagine that the glutaracetal provides those in an aqueous solution, and that absorption of these compounds in low concentrations might allow the plant to assemble what it needs while saving energy by skipping a step or two." --which seems a sensible explanation, good enough for us non-chemists.

In Robert Hudson's interview with Dr Greg Morin of Seachem, Morin additionally called Flourish Excel "a low molecular weight organic compound" similar to certain "ribulose biphosphate" "phosphoglycerate" which are produced by enzymatic action from Excel. Simple sugars, like glucose and sucrose, quickly break down in the aquarium, but bacteria are too quick to scavenge them for plants or algae to be able to use them. Overdosing with Excel does cloud the water.

Quarantining plants to eliminate snails. A ten-minute bath in a solution of potassium permanganate (KMnO4), at 10mg/liter is one classic dip to free new plants from unwanted snails. An alum bath is the other.

(Excerpt from the skeptical aquarist).