Amazon Swords Not Doing Well

I've had a 20 gallon set up for at least half a year with Amazon swords and some Crypt WendtiI green. The amazon swords have never done very well and I've changed/added several things over the last few months and have not seen any improvement. Their color is dull, and the leaves seem to melt inward from the tips, leaving nothing but the structure of the plant's veins. Many of the leaves end up dying. I used to have a problem with brown algae, but it went away when I upped the lighting. Now I seem to have a different type of algae; I think it might be the beginning of black beard algae. I have several ideas as to what the problem could be, but being a planted tank novice I think it would be wise to seek the opinion of someone more experienced than myself.
Here's a quick run down of the tank:
20 gal
Lighting 1.5 watts per gallon, from 2 Zoo Med Super Daylight Ultra Sun bulbs, 15 watts each
1.5 ml flourish fert weekly
2 ml flourish excel every other day
GH and KH around 120 ppm
pH around 7.8
Nitrate about 20, nitrite 0
Stocked lightly at this time with two platies, one endler, a couple of fry, and three nerite snails
Eco complete plant substrate
40% water change every 2 - 3 weeks, evaporation is topped up in between

The Flourish Excel is a relatively new addition; I think it was started less than two weeks ago. Also, the tank is a bit dirtier than usual because I've been sick for most of July and August. I will be doing a water change tomorrow. Here are some pictures of the leaves:

 

Looks like a few defiencies, someone else can identify them. I would suggest putting root tabs (flourish tabs work well) by the swords because eco complete doesn’t really contain enough nutrients to feed amazon swords, especially over half a year.

 

Root tabs are a must with swords.

 

Root tabs by seachem are real good. They healed my swords

 

Eco complete is an inert substrate. As said you need to put root tabs in. I would also get the seachem potassium fert to dose as well. Cut the dead/dying leaves off as they won't repair and the plants can put energy into new growth and the more healthier leaves.