Plants and Discus: What They Need to Thrive

By Alesia Benedict

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First, thank you so much for your emails about my first article in Conscientious Aquarist.  I am glad so many of you are looking forward to my future writing and that many of you have a real interest in planted tanks, discus, and planted discus tanks!  Most of my "fish pals" are not into any of these, and it is great to hear both from fellow "wet thumb" wannabes and discus-keeper wannabes alike!

At the end of my previous article, I said I would next discuss two things: plant needs and the truth behind all the horror stories on keeping discus.  Let's talk about plant needs first.

In short, most plants need three things to survive/thrive: 

• correct lighting and water temperature

• gravel/substrate (unless they are floating plants)

• food of some sort

All three of these needs must be met and must be balanced for planted aquaria to thrive. The reality of Plant Success 101 is that all  things need to be correct, in balance, and constant.  Without that foundation, you'll eventually end up with dead plants, algae gone wild, and a spouse insisting you "take down that eyesore right now!"

I'm here to help you avoid all that!

In this issue of Conscientious Aquarist, we're going to look at proper lighting for plant success.  In future issues, we will address substrates and food.  Now, I get to pat myself on the back.  I've come a long way from how I first determined the correct lighting for my tanks (if the plants died, I added another strip light; if algae got out of hand, I took off a strip light). There is soooo much confusion with "lux" and "lumens" and watts that it makes the newbie "wet-thumber" run for plastic plants! Although a few numbers will be mentioned, I promise you won't need to know Boolean algebra in order to properly light your aquarium.

Let's first consider how plants use light. Photosynthesis is the process that plants use to convert light energy into biological energy in the form of sugars (Photo = light, synthesis = to make).  Photosynthesis occurs in chloroplasts, which are components of the plants cells that contain chlorophyll (and/or other photosynthetic pigments).  Chlorophyll uses light energy to convert water and CO2 into sugars, with oxygen as a "byproduct."  These sugars are the fuel that plants use to grow.  The rate of photosynthesis can be limited by the availability of CO2 and nutrients, but we will discuss those in future issues.  Suffice it to say that no amount of light increase will improve plant growth as long as CO2 and nutrients are limited.

One of the ways to avoid disappointment is to know the types of plants that will be kept and their lighting requirements.  Not all plants are created equal when it comes to lighting!  For example, dark green plants typically possess an abundance of chlorophyll and can be grown in low light tanks.  Plants with light green leaves are typically less effective at photosynthesis, because they have less chlorophyll.  To compensate for this, light green plants usually require brighter light than dark-leaved plants.  Red-leaf plants actually reflect light rather than absorb it. They use a less effective carotenoid pigment rather than the usual chlorophyll pigment which is why they require very bright light.

Sometimes, just by moving a plant to a different light intensity, it will do much better.  This is important because with the wrong lighting conditions, even reportedly "easy" plants fail. I like to tell the story of my own adventure in this regard: When I first set up my heavily planted discus tank, I used a variety of plants, including Microsorium pteropus (Java fern), which I was told was an excellent beginner's plant -- easy and hardy.  One retailer even told me "If you can't get Java fern to grow, Missy, then you should give up on aquarium plants". I purchased some plants and took great care to thread them to some bogwood, arranging the pieces quite nicely. Within a short period of time, all the other plants in my tank took off -- but the Java fern turned black and died. Unbeknownst to me, the lighting was too intense for the Java fern.  This is a clear reason why I always say not to give up if you don't achieve immediate success! Often, just by replanting a Cryptocoryne species under the shade of another plant's leaves will make the crypt soar, whereas bringing a Swordplant species into bright light will have a profound impact on its growth rate.

There are several types of lights and fixtures from which to choose. In my tanks, I use compact fluorescents for deep tanks or those that are run with CO2. I use standard fluorescent strip lights for shallow tanks and those without CO2. One note: in general, fluorescent lighting discharges the light in every direction, thus wasting a good portion of it. You can get reflectors for such lights, and this will greatly aid in redirecting the light right into the aquarium.

Light can be measured in several different units. We will talk a bit about each of them and I'll tell you what I use to determine the correct lighting for my tanks, though others may disagree with my tactics.

Lux is a measurement of the intensity of visible light reaching any surface. Depending on the species, aquarium plants need from 300 to 6,000 lux.  Many lamps are rated for the number of lux they produce, but it is difficult for the hobbyist to account for how far away the lamp is from the aquarium and other factors. I'm not a big fan of knowing a lot about lux, so let's move on.

Light intensity can also be measured in lumens, another term often heard in lighting discussions. Just as car motors speak in terms of horsepower (the power derived from one horse), lumen was defined historically as the amount of light given off by one candle. Lumens don't do it for me, either though.

Watts is a unit of electrical power, not light output. The efficiency of a light source can be measured by the amount of lumens produced per watt. Fluorescent lighting is popular because more of the electricity (watts) is converted into light and less to heat.  In fact, fluorescent lamps produce almost double the amount of light per watt than standard incandescent lamps.

There! Isn't that simple? And I haven't even gotten into the whole wavelength thing ... or nanometers ... or peaks in blue/red/yellow light ... or ...ACK!

So how do I go about lighting my own tanks? While part of it IS still trial and error for me (my plants don't seem to always read the manuals and don't always respond as they are supposed to), I use watts per gallon as my guideline. The reason for this is alluded to above: although watts is a unit of electrical power, there isn't a lot of variation in the amount of light per watt that is produced from florescent lamp to florescent lamp.  Thus, I roughly translate watts per gallon to light output units per gallon. Tanks lit with 2 or less watts per gallon are generally referred to as "Low light" tanks. Most planted tanks can do quite nicely with 2-2.5 watts per gallon.  Those tanks that are heavily planted or house light-demanding plants (red ones for example), do best at about 3-3.5 watts per gallon. There are folks who will swear you need more, but I disagree. The other thing I do to keep things simple, is to use 6500k - 8000k, full spectrum lighting. This mimics the peak lighting of the mid-day tropical sun.

What type of lighting you use is dependant on many factors, including but not limited to: size (mostly noteworthy DEPTH) of the tank; plants you intend to keep; how you want the aquarium to generally look; use or non-use of CO2; and your allotted budget.

Next time we'll talk about another need of the plant -- substrates.

Now on to discus...and all those horror stories!

My theory was blown about a month ago, as I read an article which stated that you should not have bright lighting in your tank, as these fish are happy in almost complete darkness. The article also stated that understanding the natural discus habitat aids in keeping these fish in our tanks.

My theory, by the way, was that the horror stories of discus being an extremely difficult fish to keep (and certainly ONLY for the very experienced hobbyists) were conceived when these statements were really true. In the early days, discus keeping meant WILD CAUGHT fish taken from nature. Now, generation after generation of tank-bred discus fish have created very stable fish that are used to high lighting, heavily trafficked tank spots (living rooms, dens, etc), and even being housed in common tap water. I totally agree with treating these fish very delicately if they are caught from the wild, as the adjustment to captivity must be done quite gingerly.  I also agree (to some extent) that some of these notions still come into play when breeding discus.  And please understand that I am not saying these fish are as hardy as Danios or as easy to maintain as other fish, but I do tend to roll my eyes when I hear about how "delicate" they are.  It is also true that discus will hide and be timid until they feel safe in their tank.  That's why when you first bring them home or disturb their environment, they go and hide behind a piece of equipment, a big sword, or something else. Some people think that keeping them in bare tanks makes them more bold because there is nothing to hide behind. I disagree. Personally, I like to have plants and dither fish and get the discus acclimated to their environments ASAP, never really "babying" them from the start. From the time they are very, very little, I have my hands in the tank, getting them conditioned to such things.  Hence, they start eating from my hand when they are quite young. I also think that these fish will adjust to both a planted tank and a bare bottom tank with time. I really don't think my tank bred/raised discus have too much in common with their wild pals, except the need for superior water quality, higher than normal temperatures, and a need for nutritionally rich food.

Having said all that, let me also say this:  If you want to show your discus (I don't), it is probably best to keep them in bare bottom tanks. Bare bottom tanks make it VERY VERY easy for discus to find their food and thus, they usually grow bigger than their planted tank pals. Many breeders keep young discus in bare bottom tanks and only move adults into planted display tanks. My adults are about 7 inches, whereas show champions are 10 inches or more.

You also hear a lot of horror stories about mixing discus with other fish. To this day I read article after article from people I respect who say you cannot keep any other fish with discus. Period. I disagree with that, but there is a problem when fishkeepers don't often practice restraint. When what started out as a discus tank sadly becomes an attempted community tank that DOES spell disaster! Thanks to proper quarantine and the wider availability of farm raised fishes, most of this is not so much due to diseases from other fish (which has been touted over the years). The problem with mixing in other fish with discus is three-fold: first and foremost, most fish will out-compete discus for food. Discus require a lot to eat, but they like to continually "pick" at their food. If you have aggressive eaters in the tank, all the food will be gone before the discus can start scavenging around for it (this is the #1 reason why I don't mix angels with discus). Temperature is another important factor.  Most fish cannot tolerate the higher temperatures that discus NEED to be happy. I keep most of my tanks at 84-86 degrees. Since most other fish won't tolerate these temperatures, the hobbyist who wants to put in some other pretty fish starts thinking, "Well, I'll just lower it to 80 or so, and that should be okay for them both." Pretty soon the discus get pouty, stops eating, and disaster is eminent.

Despite these problems, I have always kept other fish in with my discus.  Not a lot of variety, but some carefully chosen ones.  Mostly, my tankmates are cardinals and rummy noses, Cory cats (some species handle the heat better than others), Ancistrus cats (aka '"Bushy Nose Catfish"), and to the chagrin of many other discus keepers, clown loaches. Not what you would call a biotope! The one fish I DO NOT ever keep with my discus are plecos (except for the very small clown pleco), as plecos have been known to attach themselves to discus, attempting to suck off their slime coating. 

We'll continue next time with more on planted tank substrates!  Until then, keep it underwater.