Plants Needs Vs Plant Mass

[wslinky]

I noticed on this forum that people are saying that the plant mass is what determines the amount of light that you use. My understanding was that it doesn't matter the number of plants but the type of plants.

If you have a tank with nothing but low light plants(ie Crypts, Anubias, Java Fern, etc) then you could easily fill the tank and have all the plants thrive with 1 WPG. Everything would be slow growing, and you wouldn't have to fertilizes.

However if you had a tank with high light plants(ie Glosso, Riccia, Ludwigia, swords, etc) and only had 1 plant the plant would not survive with 1 WPG, you would need 2-3 WPG at least. Once you get above ~1.5 WPG is when you start needing to add CO2 and Ferts since usually the higher light plants use more of the nutrients. Also with more WPG everything will start growing faster (no matter whether it is high or low light plant) so more nutrients will be needed.

My current tank is and 80 US gallon with 260w of CFL over it which gives me 3.25WPG, running 12 hours a day. I have a very light plant load, 2 Swords, a Bunch of Hydro Wisteria, a bunch of Ludwigia, 2 Anubias, 3 Crypts, 2 Lace Java Fern, and a Bunch of Pennywort. I have only had the tank up for 6 weeks and have only had fish for 2. I am fitting algae now since the 1st 3 weeks I didn't add any ferts or CO2 and ran the lights, I have been dosing ferts now for about a week in a half. The DIY CO2 has been hooked up for about 3 weeks. In the last week since I started dosing I have noticed a major decline in the algae, I have also noticed the type of algae has changed.

I would like to know the theories behind the amount of plants determining the amount of light. Unless the plants are shadowing each other then all the plants should be able to get the light wether it is 1 WPG or 4 WPG.

Thanks

 

[aaronnorth]

it does & it doesn't!

it does because if you had say rotola macranda covering 10% you will still need 2wpg+ but then you will not have enough plant mass to use all the light and algae will start to grow so it works both ways. For best results, aim for 75% coverage.

 

[Colin_T]

never heard of that but it has a bit to do with the number of plants and what type they are.

The WPG (watts per gallon) is more to make sure there is enough light getting to all the plants in the tank, particularly those at the bottom. More powerful lighting is needed to get sufficient and suitable light to the bottom of a tall tank than a shallow tank.
Plants like Rotala macranda can grow under 1WPG if they are floating on the surface. But if they are in a 2ft tall tank then they need more intense light to penetrate the water to where they are growing.

 

[SuperColey1]

As stated below lights determine which plants you can have (although some of us can find exceptions)

1WPG can grow a full tank of low light plants no problem at all. Light does NOT determine wether you need ferts or CO". This is determined by what your routine is.

For a non CO2 tank there should be no water changes to maintain CO2 stability therefore if you change 20% weekly you WILL need CO2 unless you are very lucky. Once CO2 starts being added the plants will grow a little faster and therefore you will need to add some ferts as the fish will not supply enough for this extra growth.

The non CO2 method is what Diana Walstad talks about and is know as 'EL Natural' (Not to be confused with EI.)

With all planted tanks you really need a high % of substrate coverage if you are adding anything so lightingwise you MUSt stay at the minimum for a 'few' plants and even then may struggle to keep them in shape.

The old WPG rule is a bit past it these days because it gets people thinking they need 3-4WPG to grow some plants. This isn't true unless you have a Nano. In most tanks 20G+ 2WPG will grow virtually anything as long as your tank is under 2ft tall (just as Colin states above)

Therefore plantmass and lighting are linked but plantmass doesn't determine what light you need. 1WPG can have 1 plant or the whole tank but 2WPG is asking for algae if you dont have 75% coverage.

Andy

 

[wslinky]

That makes sense, I see how if you only have 1 high light plant in a tank there will be extra nutrients. Thanks for the information.