Here is the success or failure of your planted tank can happen.

There is a formula called “Watts Per Gallon”that can provide you how many watts of lights you need to grow most plants. Normally, 2.5 – 3Watt per gallon is sufficient to grow the majority of plants available that require “Moderate” light. However, this rule only applicable only if you are using standard aquarium sold by local fish shop. If you have a custom made tank (like my tank is 8inch taller), you need to add in extra light power.

Don’t know how to calculate your aquarium volume?
Try this >> Aquarium volume calculator
Note: This calculator is not EXACT your aquarium volume. When you add in gravel and rocks, water volume decrease.

To further explanation, i am using standard 2 feet aquarium as scenario.
So 2 feet aquarium has 24″x12″x12″ = 15gallon water. Requires approximately 45watt of light.
Let’s do some calculation, if you are using T8, 16W x 3 is good. Common casing only can fit 2 x t8. So you need 2 casing. You have to take care of the space on top of your aquarium as well, 2 casing will cover almost whole top of your aquarium?

Since Malaysia are using cm and liter unit, this formula might be more useful for those confused about feet and gallon.
To calculate light watt for your aquarium, use
Aquarium height (cm) x width (cm) x water depth (cm) / 1000 = light power (W)
This formula is same as previous, using 1Watt per liter.
Example: 2feet aquarium has 60cm x 30cm x 30cm / 1000 = 54Watt light.

There are alternatives for light system in planted tank. Most common bulb used in planted tank would be T8, T5, T5HO, PLL, CFL, MH and LED. Some bulb output high density of light but also great heat is generated. So cooling system like DIY fan must be install to cold down water temperature. Different bulb also has different life span. Kindly refer to shopkeepers before you decide which kind to buy.

From top to bottom: 1.PLL, 2.T8, 3.T5

6500k or 10000k color temperature light bulb is suitable in planted tank.

General calculations:
2feet aquarium, 24inch x 12inch x 12inch, 15gallon water, 45 Watt light
3feet aquarium, 36inch x 18inch x 18inch, 50gallon water, 150 Watt light
4feet aquarium, 48inch x 18inch x 18inch, 67gallon water, 201 Watt light

Thanks for reading! šŸ™‚


29 responses »

  1. echiro says:

    Hello weijie.
    I’ve setup my aquarium and now it is around 2 weeks old. The plant i’ve planted are eleocharis acicularis, rotala red, comboma, riccia, moss and pellia.
    Rotala is the fastest plant that grow in my aquarium and secondly is riccia and others still growing but slow. The problem here is, eleocharis acicularis is starting to become yellowish and brown.

    For your information, my detail of the tank is:
    -49cm x 35cm x 35cm
    -injected with Diy co2
    -RS Hanging lighting
    I have calculated that I need use minimum 60watts light right?
    but, my light just can only support till 35watts. I’ve search on many LFS to replace the bulb with higher watt but failed.

    And additional information, there is no algae bloom in my tank and the ammonia level is very high although I have put bacter 100.

    Is that problem is because of the light?

    • WeiJieTew says:

      eleocharis acicularis is high light demanding plants. make sure you have at least 50w, if you calculated your tank actually needed 60w.
      ammonia spike is very common because we are using ADA soil which has lots of nutrients. Just do water change 30% every 3days for the first month.

      • sptan says:

        Hi Wei Jie,
        Thanks for the info, something to ask you, if I go out for vocation let’s say 2-3 weeks. Do I need to turn ON my light system for the whole 2-3 weeks ? How can I turn it off automatically ? Thanks.

      • WeiJieTew says:

        hi sptan,
        use timer. you can get it from electrical department in jusco/giant/ tesco. it cost about Rm15 each.

  2. WeiJieTew says:

    hi sptan,
    we dont care. as long as you give them 8hours light everyday then it is ok.

  3. sptan says:

    Do I need an aquarium cover ? because the shop told me normally they don’t install cover if u plan to aquascaping your aquarium because it will produce heat to aquarium. I plan to install aquarium cover instead of no cover, is that ok ? For filter side, I plan to install cheap filter ( about RM20 only ), it’s normal filter.

    • WeiJieTew says:

      you already know the reason why we dont put cover. if you insist to use then it might cause your setup to fail.

      you can use cheap filter but it doesnt provide good filter system for your planted tank.

  4. sptan says:

    If I put a cooling fan on the cover, it’s ok ? what’s your opinion ? advise ?

  5. sptan says:

    Put the cover because it look more tidy… šŸ™‚

  6. Lenk says:

    Hi I read through all your calculation and find that is something wrong example you saying the 2feet tank in inches is 24x12x12=45watt and in cm is 60x30x30=54, now it is very confusing weather is 45watt or 54watt which one should follow…?
    Please clarified, thanks

    • WeiJieTew says:

      hi Lenk,
      we are calculate the water volume inside aquarium.
      not dimension volume of the aquarium.
      Please use the link provided to know how much water does your aquarium needed. then you use 1watt light to 1liter of water.

  7. faiz says:

    i’ve 45cm aquazonic t8 15w x 2 tropical pink. is it better mix with 1 white n 1 pink or any other setup?what the difference?

  8. faris says:

    hai WeiJie.just want to ask ur opinion.if i have 2.5x1x1 ft tank,what kind of lighting suitable for my tank. ex; 2x24watt t5 / 2x24watt t5ho / 2x24watt pll or other

  9. faizjohan says:

    Dear weijie,

    Need advice on the light setup 60cm 24wx2 or 60cm PL. which will be the best to tank detail:

    -co2 injection
    -5cm soil + gravel
    1)java moss
    2)flame moss
    3)mini riccia
    4)dwarf hair grass


    • WeiJieTew says:

      hi faizjohan,
      60cm PL is 55w ? better to go for 2x24w since it generate less heat. i would recommend you to go for either sunsun 24Wx3 or Aquazonic 24wx4.
      In case you wants to put other high light demanding plants in future, you dont have to change your light setup.

  10. paul says:

    does 24wx3 t5HO meaning = 72 watts?. just want to clarify

  11. Wilson says:

    Hi, what about 45cm x 30cm x 32cm tank? Is it require 43w? Im using 11w instead of it now. Do you think thats good enough? Thanks.

    • WeiJieTew says:

      Hi Wilson,
      Calculate your water volume then you will get the light wattage you need.
      1watt light per 1 liter water is highly recommended if you want to keep medium and high light plants.
      i am selling LED light which can provide more light intensity with lower power rating.
      Thank you.

  12. WeiJieTew says:

    It would be quite pricy since you are not targetting high spec of plants.
    for your plants to grow emerse form, you can get 2 tubes of T5 bulb, they should be able to grow plants. You have to take note of your ambient temperature. It should not more than 30C.

  13. This is really good piece of information. Please keep posting good content…

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