Green Water In Planted Tank

[LordOfTheFish]

Hi! So, I've recently been having a problem in my tank with very murky green water. I had it a couple months ago, but it eventually miraculously went away, then now it's slowly come back. As you can see in the picture below, my water is seriously murky, and my tank looks pretty bad.
So, I checked an my nitrate, nitrite, ammonia, and pH are all healthy. I leave the lights on for about 12 hours a day, which I am slowly moving down to 10. I give my tank 5 ml of Flourish Excel every other day, and 5 ml of the regular Flourish every week. I recently replaced all the filter media (I know, bad move) in order to fix the problem, but that's not working at all, and it's gotten worse since then.
Is there anything I should do/stop doing to fix this? Thanks in advance to all who respond!
 

Here is a picture looking into my tank from the side. It is 4 feet long, but you can hardly see anything past 2!

 

[wet44]

The main problem is the 12 hours of light your tank is getting. I would suspect bringing that down to 6-8 hours a day will get rid of most of your algae problems. Healthy 30-50% water changes weekly is also a must for a tank of that size. 

 

[Byron]

Green water is caused by unicellular algae increasing.  This occurs due to organics/nutrients and light.  The solution is to find the balance of light (intensity, plus duration figure in) and nutrients (naturally occurring, plus any being added via fertilizers) that will provide what the specifc plants you have require, but no more (or no less).  I would have to know the data on light and plants and fish and tank dimensions to comment further.
 
When you say nitrite, nitrate, ammonia and pH are "healthy," none of us knows what this means.  Please give the numbers from your tests.  May be no issue, but at the same time we may see something from the numbers that could help.
 
Replacing the filter media was not necessarily a bad move, depending.  If the filter was dirty, this is a source of organics/nutrients, though a good rinse might have sufficed.  I tend to replace the fine white filter pads at every cleaning of my canisters, they do not respond well to being rinsed out, but the other media (ceramic disks, etc) is permanent and just rinsed thoroughly.
 
Byron.