light leaks to the water will cause this over time. the top should not be transparent nor should the sides of most hydro/aero setups. as for the leafs i never let it get that far so wouldnt be able to help ya sorry.

Any nutrient mixture that is exposed to any light source will grow algae.

You can't kill algae because it's everywhere, the best you can do is limit it's growth.

Vinci do a search in this forum for "hydrogen peroxide".
It's a very good algae controller.

Thanks guys.

My herbs cant grom much cause the algae is sticking on its root and the D.0. is below 2(very bad).

Hank_mili,
Hydrogen peroxide ....Mmm.... How much should i put?

Btw. According to my local plant expect (gardener). they suggested me to use flow through to minimize algae bloom... so im wondering how much H202 should i put?

h2o2 at about 500ppm controls both algae and other pathogens.

I tablespoonful of 3% H2O2/gallon of water.

Hi Vinci

The dosage recommended by Willard is a good "maintenance" level. BTW that should be a per week dosage. Dosage will depend on the amount and intensity of sunshine in your area.

I usually mix one Tbsp. of H2O2 per cup of water then pour it over my medium (I use lava rocks and the drip technique). This helps control the algae growth on top of the medium. I have not observed any adverse affects on my plants (tomatoes and peppers) doing this. Some plants may be more sensitive so observe any changes if any if you do this.

If you have algae on your roots already you might want to soak your roots in plain water with an H2O2 level of 1000 - 1500 PPM for a day or two then replace it with your usual nutrient solution. I've done this with my tomato plants and it seemed to have worked. Oh and be sure to thoroughly clean out your pot and soak it in an algaecide. The kind of algaecide to use is discussed on previous threads in this forum.

Not sure what you meant by "flow through" in your previous message. I'm guessing it means using an open system where the nutrient is passed through the plant and is then discarded along with any free floating algae. My opinion is this in unnecessary.

thanks...i'll try that and see what's the result.

It might be a good idea to completely clean out your system before treating with peroxide. You might need to use a peroxide or weak bleach solution to clean it out. While you are cleaning it out, make sure you have installed the light protective measures, as discussed above.
If you have a low DO, you might consider getting an additional or better air pump. I recently purchased a commercial air pump, & the difference is dramatic.
I also live in a high sun area & have come to the conclusion that using no media or a media that is not algae prone is best for me. If you are going to use a strong concentration of peroxide, experiment a bit first. I have killed tomato seedlings with too strong a concentration.