General Guide to Low-Light Planted Tanks

  • #1

Hello Everyone

Every now and then, we see various posts/questions relating to information about planted tanks such as lighting, substrate, and types of plants suitable for particular setups. To make it clear and less confusing for everyone, I am including here a brief beginner's guide to the planted tank. Please keep in mind that I am by no means an expert in this field and that I am merely providing you with some very general and basic information on how to plan for your planted tank.

Please remember, this particular guide is intended for the very beginners and not for planted tank experts! I personally have still much to learn from the experts themselves.

The three most important factors one should take into account when setting up a planted tank are (1) lighting, (2) substrate, and (3) the plants themselves. In addition, there is a fourth very important factor, which is CO2. However, I am generally speaking of low-light planted tanks here that don't require CO2 injections. This is a guide for the very beginners, and most beginners don't use CO2.


There are generally three categories of plants: low-, medium-, and high-light plants. Some plants fall in between the three categories. Lighting needs to be adjusted to your tank size and to your plant kinds. Therefore, if you choose low-light plants, you should have a low level of lighting. Most standard lighting fixtures (the box that holds your aquarium lightbulbs) provide a level below 1.0 watts per 1 gallon of lighting (wpg). While some low-light plants may survive under such lighting, most won't. If you are planning to have many plants, it's better to invest in better lighting. Low lighting is generally anything between 1.0 wpg and 2.0 wpg. If you'll have just a few low-light plants, maybe you'll make it with 1.0 wpg, but if you want more plants, I think at least 1.5 wpg would be much better. You may be able to grow some medium-light plants under 1.7 wpg too. So, generally, 1.0/1.5 - 2.0 wpg is considered to be low light. If you go above 2.0 wpg, you'll need CO2 injections at this point. Higher light speeds up the plants' metabolism and it therefore increases their need for CO2. In low-light tanks this is not a major concern, but lack of CO2 certainly is a concern in medium- and high-light tanks. What I am basically saying is that you WILL be able to grow live plants in your tank even without CO2 as long as you keep your lighting at or below 2.0 wpg and not below 1.0/1.5 (depending on the plant types).

You can calculate the lighting required for your tank by dividing the total number of Watts of lighting over the size of your tank. For example, if I have a 30 gallon tank and have a single-bulb fixture over it that is 20 Watts, this gives me a lighting level of only 0.6 wpg (20 / 30 = 0.6) - which is way too low for most aquarium plants. If, however, I have a double fixture with each lightbulb being 20 Watts over the same 30 gallon tank, this gives me a total of 1.3 wpg (40 / 30 = 1.3) - which is much better.

Most standard fixtures come with standard fluorescent lightbulbs, which have very low wattage usually running around 20W or so. However, there are double lighting strips with standard fluorescent lightbulbs, which - when combined - provide enough lighting for low-light tanks. There are also compact fluorescent fixtures with compact fluorescent lightbulbs, which provide much better lighting due to higher wattage. This c.f. lighting is referred to as High Output lighting (HO). This lighting type can be used over both low-light and medium- to high-light tanks as an addition to existing lighting. You basically can use only standard lighting (using more than one lightbulb in your fixture), only c.f. lighting, or a combination of the two - whichever option suits your needs best. Lastly, there is a lighting type called Very High Output (VHO) lighting, which is really for high-light tanks and plants. These are usually various strong metal halide lamps as well as other powerful lighting devices. For a low-light tank, we need to be concerned with standard and c.f. (HO) lighting only.

Now a little bit about standard and c.f. aquarium lightbulbs. There is another measure of effectiveness of aquarium lighting expressed in a lightbulb's "Kelvin" temperature (marked by letter "K"). Some lightbulbs are more suitable for planted aquaria while others are specifically for saltwater reef tanks. The reason you see all saltwater tanks with blue lighting is that they have lightbulbs with a lot of blue spectrum in them. While this blue lighting is beneficial to saltwater reef tanks, it would be possibly disastrous for a planted tank. The blue spectrum in lighting encourages algal growth. If algae cover all of your plants, the plants will no longer be able to receive light, and will therefore die. The blue lighting has a very high Kelvin temperature, and the light color leaning toward a more yellowish spectrum has a lower Kelvin temperature. has a very clear and informative description regarding the lighting spectra for c.f. lightbulbs, but they can be equally applied to standard lightbulbs. Here is a picture of the lightbulbs and their spectra: , and here is an explanation of what they all mean:

As this article says, "6,700K daylight white bulbs are generally the brightest of all the bulbs. The color of this bulb tends to be more of a yellowish/white bulb. Plants tend to thrive under this color temperature." This is also the spectrum I personally use over my low-light planted tank (without any CO2 injections) and my plants are doing very well. This, of course, doesn't mean you "have to" have this particular spectrum. You can have anything between 6,700K and 10,000K (on the picture from MarineDepot) for a planted tank. You can even have a lightbulb that is below 6,700K, although I am not sure if it will provide successful plant growth ... but it may very well do so. Any lightbulb above 10,000K (that is ACTINIC) will have too much of the blue spectrum for a planted tank, so avoid it in order to prevent excessive algal growth. Chances are you'll always have algae, but you'll have much less algae with a lightbulb at or under 10,000K than with a lightbulb over 10,000K/ACTINIC. Whatever the small amounts of algae you'll have, your algae eater(s) should take care of them.

The distance of the light source to the plants counts as well. However, I will give you some links to read up on it, as I am not very fluent on the subject. Here: and .


Depending on the plant types as well as on the amount of plants, either plain/inert gravel or some nutrient-rich gravel/substrate can be used. If you will have only a few low-light plants, you can go with a regular gravel and use nutrient-rich tablets for plants (plant tabs), placing the tabs as near the plants as possible without disturbing the plants' roots. The tablets are buried in the gravel. Some plants such as Anubias, Java Fern, and Java Moss don't even need any gravel as they're tied to objects inside your aquarium (for example, tied to driftwood). You can use fishing line or black cotton thread to tie plants to various objects in your tank. These three plants are all low-light. If, however, you want your entire tank floor planted with rooting plants, then it's best to simply get a nutrient-rich substrate. The best known commercially available nutrient-rich plant substrates are: Fluorite by Seachem, Eco-Complete by Carib-Sea, Amazonia by TakashI Amano, and 's own substrate. Of these four substrates, Fluorite and Eco-Complete seem to be most popular. Before you buy any of these substrates, you should read more about them to make sure they meet your needs.

Fluorite: seachem flourite

These nutrient-rich substrates will provide an excellent growth medium for your plants. Depending on your particular needs, you may also mix nutrient-rich substrates with regular gravels (in combination with or without plant tabs). There are really countless possibilities. For more detailed information about aquarium substrate and its functions, read this article: ("Substrates for Aquarium Plants"). Lastly, some people argue that plain backyard soil can be used to grow aquarium plants successfully. While it does hold true for many people, I'd advise you to read "Ecology of the Planted Aquarium" by Diana Walstad BEFORE setting up a tank with plain soil. It is a very interesting book - definitely worth reading.

Note: If you decide to go with Fluorite, please read this article on how to rinse it properly: How to Wash FLUORITE

In a planted tank, the depth of substrate should be 2.5" - 3" with the front at 2.5" (for small plants) and the back at 3" (for large plants). Here is a very useful substrate calculator:


As mentioned above, there are generally three categories of plants: low-, medium-, and high-light plants. Some plants fall in between the three categories. For a low-light tank, we're mainly concerned with low- to some medium-light plants.

Now, as I've said earlier, the three great low-light plants that do not even need any substrate are: Anubias, Java Fern, and Java Moss. Other low-light plants are: Water Sprite and Hornwort, plus perhaps some Cryptocoryne, Hygrophila, and Sagittaria species. If you will have lighting between 1.5 - 2.0 wpg, you should be OK with Cryptocorynes, Hygrophila, and Sagittaria ... as well as with Water Wisteria and even with some medium-light plants such as Vallisnerias, Swords, and certain Aponogetons. For more information on aquarium plants, I strongly recommend a book called "Aquarium Plants" by Peter Hiscock or "MinI Encyclopedia of Aquarium Plants" also by Peter Hiscock. The same author has also written an excellent book on how to set up particular biotopes (including lots of planted tanks). This book is called "Aquarium Designs: Inspired by Nature".

If you'd like to see some breath-taking s of planted aquaria, you should see all three of TakashI Amano's "Nature Aquarium World" books (I, II, and III).

And one last point: The fish load in a planted tank. Fish load needs to be taken into account when setting up a planted tank as well. If you have too many and/or too large fish, they'll produce too much waste for the plants to consume, thereby causing algae. On the other hand, too few fish won't provide enough waste for the plants to consume, thereby causing algae too. How so? Having little nutrients, plants grow slowly and then start to die and decay. This decay of plants will create nutrients for algae and will thereby give algae an opportunity to take over the tank. So ... you also need to find the correct fish load in your tank. The general idea is for the plants to grow at such a rate that they'll consume all available nutrients, leaving algae with nothing to feed on and therefore to die.


Whew ... OK. I think this will be enough for now. Like I said, it's a very general guideline/introduction to a low-light planted tank. However, I hope it will provide answers to many of your questions as well as disperse the confusion surrounding the issues of lighting, substrate, plants, and fish load. Just remember: Not one planted tank is the same, and every tank has its own life. You need to find the correct balance between all the elements involved - lighting, substrate, plants, and fish load - so that your planted tank is successful. You need to discover for yourself whatever works best for YOU. Just because something works for someone else, does not mean it will work for you, and vice versa. Trial and error will be unavoidable but they'll add up greatly to your planted tank knowledge and experience.

Best of luck to all of you!

  • #2
Wow, that was good, thank you... but now I have a question: My lights have T5 tubes, the really thin ones, and a couple people have told me that they'e actually more efficiant and the WPG has to be calculated differently... have you ever heard this before? Because right now, as you already know, I'm peaking between 1.8 and 2.2 wpg, based on just what the tubes say the wattage is. But if for some reason it's actually figured higher, then I might be getting into the CO2 diffuser range. Anyway, ever hear of such a thing?
  • #3
T5's are very efficient because of their shape.

I don't have a scientific formula, but in my experience, a HO (high output) T5 lighting fixture with 4 x 54W HO tubes is more light than 4 x 65W power compact fluorescent.

If you have 1.8 to 2.2 watts of high output T5 lighting, I would get some CO2 running.
  • #4
can I replace the bulbs in my standard ballasts that came with my 55 with 6700K bulbs without complications?
  • #5
Yes, as long as you use the same type of bulb (T-8, T-5, etc).

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