prairielilly

I have a 20g tank that came in a Marineland starter kit along with a fluorescent hood. Recently the ballast on the light started to hum a lot and I replaced the hood with one nearly identical. The tube was fine on the former light and is identical to the new one - they're both Marineland Eclipse daylight tubes, I think they were called T8-15 or T15-8? it's an 18" tube and has 15 W, meaning the light in this tank is 0.75 WPG. No idea about lux or anything like that, but the tank is approximately 24 x 12 x 18" (LxWxH) if that helps. The light works and is bright enough for my tastes, and there's still the old tube that also works, so I'm not really interested in replacing the light, but I thought 0.75 wpg wasn't enough light for most plants? or am I wrong? I was thinking of having java moss, java fern and anubias. I have also noticed that my tank has really, really low nitrates (never seems to get over 5), so I'm guessing I would need to fertilize heavily - should I just stick with silk plants?

Llama

Usually you'd go with 2 Watts / gallon

Anubias doesn't need a lot of light, so I think it'll be good over there.

Anubias is also slow growing, so it won't need much Nitrates (Nitrates are mostly used to make proteins)

Java fern is quite hardy too. DOn't know about java moss.

prairielilly

I know I'd usually need 2 wpg, but I had done some reading that said it wasn't so much the wpg as the 'lux' or the combination of light intensity/time on/distance from substrate/tank surface area, and I would find it hard to believe with how many Marineland Eclipse systems are out there that no one has ever tried to grow live plants in them. I just would rather find out now than spend a bunch of money on plants and have them all die. I looked at a few websites for LFS's selling light tubes and the vast majority of the 18" tubes were also 15 W, many didn't even specify.

Nate McFin

Java fern and moss as well as anubias should all be fine. FYI though...turning a lower watt light on longer doesn't work. Only thing it might do is encourage algae. Any idea what the Kelvin rating is for the bulbs?

Master Snake

I had the same problem as the two hoods that came with my 55 would only hold 18" 15 watt bulbs. I first used two brand new bulbs that were $20 a piece, only to return them and go to the Home Depot and purchase a fixture that would allow for 1.5 watts per gallon (probly more since I have substrate, driftwood, and loads of rocks). The fixture and 6500k bulbs were only $15! Great deal! I know I probly don't have perfect reflectors or that kind of business, but I feel safe in saying it was better than my previous lights.

prairielilly

Master Snake: ok, but how do you get it to attach to the tank? I have 3 cats... and doesn't it have to be water-resistant or some such?

Nate McFin: no idea on the Kelvins. It's not written on the bulbs, just says 'Eclipse Daylight T8 15W'. Ideally should be 6700 K if I'm right? I know longer hours doesn't equal more intensity, I'd just seen that included as part of the light requirements calculation for plants. Something like Kelvins and surface area and distance to substrate, divided by some factor taking into account time on...wpg works for me! My lights are usually on up to 16 hours a day but that's just due to my crazy schedule (and yes, I do get algae bc of it).

I did find a store where I could buy a proper-wattage bulb (I think) but it was $35, and I'm wondering if higher wattage in a fixture made for lower wattages is bad? sure is in household electrics. The first one blew the ballast in less than 6 months as it is and that only got normal use.

I'm currently redoing my tank and thought it would be a great time to go from silk plants to live, but I just replaced the light so I really don't want to have to do so again. If I did use those species mentioned and had this low light, would I need fertilizers? and if so is it better to use root tabs or water column solutions?

Thanks so much for all the help!

Master Snake

Well the fixture I purchased gave me the option of hanging it from the ceiling. I can see how one would not find this method suitable so I got myself some L joints. I attached those to the fixture and then on the bottom to a sturdy block that i set on the glass hood. I really wanna add some sort of reflection to surely maximize the light efficiency.

Nate McFin

Yeah definately don't want to overdo the wattage.
Water column ferts for those plants as none are root feeders. You won't need to use a bunch either because the plants won't be able to use as much without higher light and Co2.
Liquid ferts (something along the lines of Seachems Flourish and small doses of Flourish Excel should do the trick. Small is the word to remember.

snowball

lighting is not based on how bright it is but rather the lux and kelvin
Bulbs with high lux and kelvin are less bright and usually let plants absorb more of the lights due to the color output so basicly it would look rather dim to you but plants absorb more of the light. Find out the kelvin and lux of the bulbs then you can decide what plants you can keep.

mathas

I'm going to have to disagree

Lux is a measure of light intensity, so I'm not sure what you mean by high lux = less bright. One lux is defined one lumen per square meter, and would be a measurement how much light is actually getting to a specific plant or other point of interest in the tank. Since this metric is influenced by a number of variables (reflector, water depth, shadows, etc.), it would be impossible for a bulb to have a measurable lux rating. One could purchase or borrow specialized equipment to measure the lux rating at various places throughout the tank, but it's not a value people can just "find out" by looking at a bulb's packaging or a manufacturer's website.

I also think the Kelvin rating has almost no benefit when it comes to making a decision of a bulb's suitability for plant growth, as what color the light looks like to human eyes has little impact on whether or not it produces light in the appropriate spectrum for plants to use. It's also completely unstandardized across the industry, a 6500K bulb from one company may not put out the same type of light as a 6500K bulb from someone else. I run bulbs that are billed as 9325K, but they actually emit a pinkish light rather than the blue one might expect from a Kelvin rating of almost 10,000.

prairielilly

In physics, chemistry, geology and every other branch of science, 'Kelvin' is a measure of temperature. I convert Kelvins to Celsius to Fahrenheit all the time. Therefore I have been a little confused with the aquarium hobby's use of Kelvins to describe light colour - the colour temperature. As I understand it, the temperature in Kelvins will correspond to the heat output of a particular wavelength of light, which has a corresponding colour. I don't know that two different wavelengths of light (with two different temperatures = heat outputs) would have two different colours. Just thought I'd mention that that is a bit confusing.

As I wasn't about to buy yet another light for this tank I recently aquascaped it with silk plants. I may or may not try some java moss on the driftwood here. Someday I hope to get a 55-60g and, with all this newfound knowledge about light requirements buy a light for it that will actually allow me to grow something.

mathas

It's not just the aquarium hobby, it's the lighting industry in general

My understanding is that a bulb's color temperature means it should produce exactly the same color light as a theoretical black body heated to the same temperature (as it heats, this black body emits light that follows the locus line shown here). In other words, a 6700K light and a black body heated to 6700°K sitting right next to one another should emit the same color light. But as the APC quote I posted mentions, that doesn't necessarily mean that manufacturers accurately market their bulbs with a true color temperature rating. That's part of why I feel it's such an over-hyped metric.

If you're looking at only color temperature, just about any bulb with a rating between 5000K and 10000K will probably be fine for a planted tank... if you get more granular than that and worry about 5500K vs 6700K, you're mostly deciding how the bulb will look to you rather than basing the decision on suitability for plant growth. There are probably minimal differences, but in my unscientific opinion, I doubt those differences are enough to have any meaningful impact on the decision. I could be wrong, but I'd have to see actual experiments conducted rather than anecdotal evidence before I was convinced otherwise.

prairielilly

Thanks Good info to have on hand when MTS strikes again and I start dreaming about my wonderful lush planted tank...