Plant problems

[nighthawk]

Hi, plant gurus. I have had my tank going for about a year, and I am noticing a problem with the stem plants. My Bacopa and Alternanthera are looking like palm trees, with lots of stem growth and no leaf growth.

I have changed very little about the tank since starting. The substrate is a mix of fluorite and gravel. Lighting is just over 2 wpg, excel as carbon source dosing as per bottle instructions. I fertilize with Tropica master grow weekly, and do weekly water changes. I have replaced the bulbs about a month ago. I also use Tropika substrate pellets.

This has been a gradual change over the last several months. I am not sure if the plants are just outgrowing their usefulness, or if there is a problem. The vals, swords and cabomba in the same tank are growing like stinkweeds.

Any thoughts would be appreciated!

[werner]

I'd guess it's mostly light related. Since you've already replaced your old bulbs, that's not the issue. What type/brand of bulbs are you using? The specific wavelengths of light emitted by the bulb plays a big role- lots of red light results in longer stem length between nodes, while blue light encourages more compact growth.

Also, since they are getting plenty of nutrients, they're racing to the top of the tank for more light (both species like high light levels.) Has your tank temperature has increased slightly now that it's warmer out? That may contribute a bit too.

[jvision]

I agree that it's either light wavelength, or perhaps the lower parts of the plant aren't getting enough light. Is higher growth still close together?

[jbot]

my first thought was light as well.... 2 wpg is a bare minimum. Are your leaves red? Bacopa and Alternanthera require medium to very high light. If your light wavelength is in the 5000-10000K range you should be OK (although 6700K is ideal).... Give us your lighting set up specs.

If it's not lighting, then it's likely a nutrient deficiency.... These plants require a steady dose of iron to the water column.I've never used Tropica ferts before (or any liquid fert for that matter) - is there ample supply of iron, N, K, and P?

Finally, your Excel dosing COULD be affecting the growth of these plants (pure speculation).... Have you considered a DIY CO2 setup?

[nighthawk]

Thanks for all the thoughts. I have pruned some of the taller cabomba, which certainly were hogging a bit of the light, and I am hoping that will make a difference. The lighting is Coralife Colormax, 2 X 96 watts and another 40 watts of a bluer spectrum (T5 that would fit over the rest of the space in the back of the tank) over 92 gallons. The leaves do have a nice red colour on the alternanthera, and I have noticed improvement of the colour of the leaves on the sword plant since changing to the redder lights (colormax). The fertilizer doesn't contain N or P, but I have enough fish that those nutrients should be taken care of in other ways.

I will see what happens with a more open surface; thanks for your sage advice. :bow:

[jvision]

If you have more than 2 wpg and CO2, then you really should add NPK, IMO. If you can find a source of dry NPK, it'll be a lot cheaper than going with one of the liquid brands.

[werner]

If your light wavelength is in the 5000-10000K range you should be OK (although 6700K is ideal)

Don't confuse color temperature with light wavelengths. The CCT (Correlated Color Temperature) represents the overall appearance of a bulb- at 1000K it looks red, yellow at about 1500K, white at 5500K, bluish-white at 6500K and more bluish at 10000K. For aquarium usage, choosing a bulb's CCT is mostly based on preference. A 6700K bulb looks sunny and tropical for a FW tank, whereas 10000K+ simulates deep ocean waters for SW. Some people prefer the bluer look on their FW tanks.

For plant growth, however, the light wavelengths which are put out by a bulb are more important than color temp. The SPD (Spectral Power Distribution) graph shows which wavelengths of light are emitted in what proportions by a bulb. Most good manufacturers put this on their bulb packaging or website. For photosynthesis, plants require light in the red and blue parts of the spectrum:

Compact fluorescent bulbs sold for household use put out a lot of green and yellow light. They appears bright to the human eye, but since there is very little in the red and blue parts of the spectrum, they don't make the best plant bulbs. Specialty plant growth bulbs have a weird purplish color that looks awful to us, but they emit the right parts of the spectrum for photosynthesis.

Don't assume that all 6700k bulbs (or 10000K, etc.) are the same:

The SPD on the left shows an incandescent lamp; on the right is a red, green and blue LED mixed spectrum. Obviously the spectral output is significantly different even though both bulbs are rated at 2856K.

There is a comparison between the Colormax 6700K and the original Coralife 6700K bulbs here. Any chance you switched from the regular 6700K bulbs to the Colormax? I have heard several other comments that the Colormax bulbs aren't the greatest for plants.

Also, you need to consider the depth of your tank. 2.5wpg on a 20gal will be better lighting than the same 2.5wpg on a 92gal. Keeping the top clear of the Cabomba should help a lot.

If you have a high fish load and feed well, you are may be able to get away without adding N and P. However, have a look here to see if the plants are showing any signs of deficiency. If there isn't much light reaching the lower tank levels, older leaves may not be there to examine. Once again, keeping the fast growing (nutrient hogging) Cabomba in check should help.

[nighthawk]

Thanks for your well-researched reply, Werner. I will do some reading, and see what I come up with. I did switch from regular to Colormax, but the problem had started before the switch, and I am really happy so far with what the Colormax is doing to the non-green colours of my plants, so I think I will give it the good college try for the year or so that the bulbs last, and then reassess.

Your comment about the depth of the tank is something I've worried about before. Are you suggesting that more light is necessary the deeper the water? I may have to go to metal halides to get much more light over the tank than I have now, and that's not a step I am willing to take financially right now, although I'd certainly consider it for the future.