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Plant fertilizers are available as liquid or substrate fertilizers. Both should only contain the micro nutrients. Liquid fertilizers have to be dosed more frequently; substrate fertilizers will last longer. Since there are no obvious differences in efficiency, it is up to the aquarists' preference which to use.

Next to the micro nutrients, fertilizers contain chelates. The chelate is an organic molecule which binds metal ions thus protecting them from early precipitation. The preferred type is abbreviated DTPA because of its stability up to a pH level of 7.5

Unfortunately some fertilizers contain the chelate EDTA, which is much cheaper. However chelate EDTA is only stable at a pH up to 6.0 and therefore mostly useless in aquariums.

What do you think?


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5 Posts
although i do now have a question, i have well water down in south florida, and my water is very high in iron. i have Flourite substrate and also the liquid Flourish (from another tank, have not used it with the substrate tank). would my high iron in the water decrease my need for the liquid fertilizer?
or am i overthinking it? lol

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742 Posts
good write up. nice easily explained information.

few questions that I have...

Will having CO2/ferts expand your effective light range. Probably confusing statement, what I mean is if I have a low light tank with ferts and CO2 will I be able to potentially keep moderate light plants in the tank? Or are light levels locked, low light plants can grow in all light levels, as if it were an upward ladder, plants can use light levels up the ladder, but never down the ladder, ie high light would never do well in moderate/low light.

I have just set up a new tank 30Xhigh. Currently my plans are mostly a planted tank with little to no fish. If there are no fish (there are a few snails) do I have to worry about CO2 levels or can I just throw a DIY system on there and not worry about oxygen levels.

Is there such a thing as over fertilizing. In a tank with or without fish ( I also have a 55 planted with fish, moderate light but no CO2) is it possible to overdose the fertilization to the point where it negatively effects plants (in a non fish tank) or fish in an populated tank.

My 55gallon (~2.3 wpg) has BBA. I have routinely started Flourish (2x week) and daily Excel. The BBA does not appear to be spreading at all in the tank, and no other algae seems to be growing. Will regular dosing of ferts and presumably healthy plants ever be enough to get rid of the BBA or once I have it even if it isnt spreading it will not go away on its own. Will the addition of pressurized CO2 cause the algae to die off? And if I add CO2 should I discontinue Excel, but continue on with the other ferts?

Edit- thought of another one. I run an airpump in 55g 24/7. It is not overpopulated, but it is probably about as stocked as I would want it, close to capacity, without overcrowding. If I ran CO2 would I be a fool to continue running the airpump, at least when the light was on? Or if it is pressurized CO2 put through a reactor, will it not matter. The air pump is a model for a 20 gallon tank, so it isnt pumping out huge amounts of air, but I had shut them off when I first started using Excel, and I guess I had a ph crash (if thats possible with Excel) I woke up the next morning and 30% of my fish were dead, got the airspump back on and within half an hour everyone that was still alive was back to normal. So I am nervous about the whole CO2 / lower oxygen level issue...

Thanks for any info you can offer...

The only thing I can't find is a small enough bottle for this the only one I can find is an old spice jar that's glass and about 3" long/ deep would that still be accurate if filled just under the top of the glue cap there will be a lot of space in there?

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162 Posts
Whilst some say higher levels CO2 do not reduce dissolved oxygen in the water (it sometimes can, depending on other factors) even moderate increases can have some fish gasping at the water surface. If it doesn't affect the dissolved O2 then what's going on?

To diffuse the CO2 out of their blood across their gill surfaces, fish require a concentration differential between the water and the blood. As the differential diminishes due to increased CO2, the gas exchange slows and stops. The fish can't excrete the CO2 and they die. This is sometimes exacerbated by aquarists 'turning off' the air stone so as to reduce CO2 loss at the surface. This the results in lowering the dissolved O2. Then the lights go out and the plants start respiration. They stop eating CO2, start using oxygen and the balance tips and in the morning you find some dead fish and it's a mystery.

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74 Posts

oK...So I just did this DIY and after a couple of hours of hunting around this was the best I could do:

Now....I didn't have the proper tool to cut a larger hole out of the top of this salt shaker I left it thinking that the holes that were already in it may work......well after a couple hours the solution is still dark blue.

Mind you, I did follow all the direction and scaled up the mixture to 30mL of distilled water/baking soda, and 54 drops of the solution from the API pH test kit (9 drops x 5)....

Do you think that this is because I didn't cut the hole in the salt shaker head to make a bigger surface area? Or do you think it may be because of the tubing I connected to the paint tip applicator up to the 'air' in the shaker?? Maybe a combination of both?

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122 Posts
Fantastic article! I'm going to be referencing it myself often and referring other to it as well! I have a few clarifications and a couple ideas I'd like to get opinions on.

First - I'm setting up a 50g heavy, i'd like to nail down the CO2 before adding fish, but dont know how much CO2 the fauna(phishies & inverts) will increase the concentration in the tank. Ie the tank begins without fauna at 20-25ppm CO2 with room for an additional 5-10ppm CO2 when the fish and such are added so that I dont exceed the recommended 30ppm.

Second - Is the drop checker a one time check that you need to refill for each reading or is it progressive?

Ideally i think it would be cool to have 2 drop checks, one with a 4dKh solution to make sure im under and one with a 3dKh solution to make sure i have enough CO2. Any thoughts on that?

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276 Posts
Sorry to revive this old thread but frankly, this and your pressurized CO2 thread, are the two absolute best primers out there.

On topic, I was very interested in your explanation about how the WPG has fallen apart (not to mention LED being a completely different bag). Simple question: How does the single 13watt CP over my Fluval Flora (basically a 12" cube) rate? I'm guessing "low light". Would a second one take me up to "Medium", or would that be getting towards what would be considered "high"?

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21,007 Posts
One problem we all have when we write up a primer on a planted tank subject is that over time the "facts" are found to not be facts. Some "facts" go from "you can swear on it" to "well perhaps under some circumstances" facts. CO2 is just one more such subject.

Years ago, the old timers learned that they could improve their aquatic plant growth if they could just get more CO2 into the water. Yeast/sugar DIY CO2 soon followed, and that method is still in use because it worked for so many different people. This encouraged people to try for still better/faster plant growth by using still more light. But, that caused severe algae problems to erupt.

Then the old timers started looking for a better way to get more CO2 into the water to help avoid the algae problem. One way that was tried was dry ice - never did work well. Another (tried by Amano) was pouring carbonated water into the tank. That worked but was super expensive and a lot of extra work.

Finally pressurized CO2, using bottles of liquid CO2 as the source, was developed into the ultimate, best of all methods for using CO2. And, that opened the door to using a lot more light, making a lot more species of plants growable in our tanks. It was soon found that if you kept about 30 ppm of CO2 in the water you had an acceptable risk of killing fish, good growth of most plants, and the CO2 usage was low enough to keep the costs and labor down. So the "holy grail" of using CO2 became 30 ppm.

But, we forgot something: DIY CO2 did work, and was very effective for a lot of people, using not just 10-20 gallon tanks, but even bigger ones.

In 2002 Ole Pedersen and others, in Denmark, wrote a scientific paper about Liebig's Rule of the Minimum, including CO2 and light, which contained a lot of useful data that explained why DIY CO2 worked so well it is still in use. In 1999 and later Diana Walstad wrote her book about her method for keeping a very low tech aquarium. In that book she included some information about the role of CO2 in a natural tank. That also was a good clue about why DIY CO2 had been so successful when first tried. But, we planted tank people were still concentrating on growing ever more light demanding, CO2 demanding plants, and we ignored what all of that information should have taught us. So, the "fact" that "you can't use DIY CO2 successfully on big tanks without multiple big bottles of yeast/sugar solutions" became unquestioned, and continues to be today.

The data in the Pedersen paper was a compilation of growth rates versus light intensity and CO2 concentration, for one plant - Riccia. That data can be plotted to show that for light intensity between about 25 PAR (very low) to about 90 PAR (very high), for Riccia, it only takes about 10 ppm to get the maximum growth rate for Riccia. More than 10 ppm does not increase the growth rate!

Diana Walstad was able to improve her plant growth by the simple method of having a long dark, resting period in the middle of the photoperiod. That allowed the natural production of CO2, by the substrate, to restore the concentration of CO2 in the water, after the growing plants had depleted it. She was dealing with less than 10 ppm of CO2 maximum.

I have found that Hydrophila cormybosa simensis, a low light, fast growing plant (unlike the slow growing Riccia) will grow very much faster with DIY CO2 at a concentration of less than 10 ppm. This was done with a 65 gallon tank, with about a one bubble per second production of CO2. Other plants in the tank, including Bacopa, crypts, vals, etc. also grew much healthier and faster with that small addition of CO2. So, my experience backs up the data from Pedersen and the method used by Diana Walstad.

It is time to stop telling people that DIY CO2 is useless on big tanks. For low light tanks, 30-40 PAR light intensity, if not more, DIY CO2 from a one bottle system can be very useful on tanks at least as big as 65 gallons. There is no reason why it would not be useful on much bigger tanks.

Today we can use a citric acid/baking soda DIY system, which is controllable, unlike yeast systems, and have a very cheap, very beneficial addition for our big, low to low medium light planted tanks.

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What about an LED light? I bought a new aquarium with lights and filters incorporated into the hood. It has an LED light.

Lighting is an important factor in a planted aquarium. It can be analogized as follows: light is like the accelerator of a car. The more light you have, the faster you are pushing down the accelerator. The less light you have, the less you are pushing down the accelerator. When you are driving faster, you must maintain your car more often, i.e. oil changes, checking your tires, and so forth.

Similarly, in higher lighting conditions, you will be "driving" your plants faster, and they will require more maintenance (i.e. carbon dioxide, nutrients, etc).

A guideline that can be used when describing lighting is the "Watt per gallon" (WPG) guideline. This is not a rule per se, but only a guideline (for reasons that will be explained below).

Lighting can be divided into 3 general categories:

1) Low lighting (~ 1 - 1.5 WPG)
2) Medium lighting (2 WPG)
3) High lighting (3+ WPG)

Correspondingly, plants can also be divided into these 3 categories, with "low light" plants being able to tolerate low lighting conditions, and "high light" plants requiring higher lighting conditions. This does not mean that "low light" plants cannot grow in higher lighting, however.

To explain why the WPG is only a guideline, one must consider the origins of it. WPG was originally designed for T12 fluorescent bulbs (i.e. bulbs that are 1.5 inches in diameter, the number after the T indicates the diameter in eighths of an inch). However, with the advent of various types of bulbs, i.e. T8, T5, power compact (PC) lighting, this guideline has become less accurate. In addition, this guideline cannot be applied in very small (10 gallons or less) or very large (maybe 55 gallons or more (ballpark figure)).

For instance, in my 2.5 gallon aquarium, I have two 13W compact fluorescents. This gives a total of 26 watts, corresponding to just over 10 WPG. This might seem suicidal at first (remember, the amount of light drives the amount of plant growth), however, because the WPG guideline is not accurate at small tanks, it turns out my 2.5g nano may fall under the "high light" conditions only (as opposed to "suicidally high light"). If I were to follow the WPG guideline strictly, and have 3 WPG over my 2.5g nano (i.e. 7.5 watts of light), then the tank would be poorly lit, and could only fall under a "low light" setup.

Not only is the amount of lighting critical to a planted tank, but the type of lighting is also important. As mentioned, there are several types of lighting available to the aquarist today (T12, T8, T5, PC, etc). Such bulbs can sometimes be confusing the novice planted aquarist. As a general rule, T8 and T5 are newer and more efficient than the older T12 bulbs. There are two camps of thought, one which prefers PC lighting while the other prefers T5 lighting, but to argue the points of these two types would be beyond the scope of this article.

One must remember that in general, fluorescent bulbs are all subject to a phenomenon called "restrike". In restrike, light that is emitted from the bulb will "restrike" the bulb, reducing the output of effective light. In general, straight fluorescent tubes are less prone to restrike than (say) the spiral power compact bulbs that can be purchased.

For some, the "colour temperature" of the bulb will also be a consideration. Plants in general are not too picky regarding the colour temperature, and some may argue that this point is not necessary, however, I have decided to briefly touch upon this.

In "normal" daylight, the sun is 5500 Kelvin (the unit of measure for colour temperature). Higher colour temperatures will appear bluer, while lower colour temperatures will appear redder. Here are some typical colour temperatures that can be found:

2700K "warm white"
3500K "cool white"
6500K "daylight"

Do keep in mind that light is but one important factor in keeping a successful planted aquarium

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For a planted tank, I have written an article (on another forums) regarding some of the things you have to consider. I will simply copy and paste it here.

Edit: Comments/criticisms/replies are most welcome; I've noticed this thread has 30+ views and not one response from anyone else!

So you decided you wanted to start a planted tank, after seeing a beautiful aquascape in the AGA contests, or perhaps in one of Takashi Amano’s Nature World Aquarium books. Hopefully the guide I’m writing here will serve as a primer to jumpstart you into the world of planted aquaria.

Before starting a planted tank, you first must ask yourself: How much work (and subsequently time and money) do I want to invest into a planted tank? Beginners sometimes forget that many tanks that they see in the AGA contests or Takashi Amano's books are high maintenance tanks (i.e. require weekly pruning).

In essence, planted aquaria can take one of two forms: those that are high light tanks, and those that are low light tanks. Regardless of the type of lighting, algae can become a problem in both types of tanks if proper care and maintenance are not observed. Another question that must be asked at this point is: Do I want a low light (and hence lower maintenance (not maintenance free!)) tank, or a higher light (and thus higher maintenance) tank?

In general, there are 3 factors that are required for plant growth:

1) Light
2) Nutrients
3) Carbon dioxide

One can imagine these 3 factors like a triangle; a deficit in one or more of any of these 3 factors will result in an imbalance, allowing algae to take advantage of the situation and begin to flourish and grow.
thank you for your hard work on this one, Dark!
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