There's an imbalance like I tried to explain somewhere earlier: Your weekly ferts PLUS proper lights PLUS proper CO2 fish has to be all in balance for plants to thrive, if one of these factors is not balanced right with the other 2 you'll see the problem you have.
We can excl nutrition there if you say you used to dose weekly and it didn't change anything. I'll also excl lack CO2 judging from the picture with the amount platy there. Which does leave your light in question.
Do you only have a single 4ft tube of this "flora glo" there? What lights did you get for the new tank?
Just so we can be sure we're all talking about the same pictures/ plants:
These are Cypts: Cryptocorynes
These are Swords: Swords
Algae generally occurs when something (again sorry) is out of balance in the tank. So if you eleimiate the factor causing some of your plants not to thrive well, you'll surly also get rid of the alage (trust me I just battled my first ever hardcore algae attack in the new 55g with like 5 diff ugly algae types).
There's tons DYI way's you can go about this for either tank. My 4ft shoo light strip with its 2 bulbs sits RIGHT on the plastic frame that's on the 55g, I built a thin wood frame all around it (see pictures under aquariums).
Alternatively if you have a glass top and just want something to "hold" lights; you can use a gutter (See this thread bottom of page adventures in budget DIY lighting
) Or you can bend whatever shape & size you want to have out of flashing yourself....options are endless. You may wanna browse throught the lighting DYI thread there, plenty of ideas to see there.
What bulb or tube you add there is secondary, whatever you can work with best. What REALLY matters is that whatever bulbs/ tubes you buy to ensure they're full spectrum lamps, a Kelvin rating between 5-6500K (see small print on packages) and right around 1wpg; if you go to Wal-Mart, Lowes, Homedepot you can find these labeled as "Daylights or Ultimate Daylights" by GE, Phillips, Salvinia (sp?). I have these as small tubular screw ins for the 10g's and as florescent strips over the larger tanks, works wonderful for me (and there's plenty other folks on here that swear by these Home store bulbs for planted tanks, simply cause its the same then what you can find at the fish store, just not $20 per bulb but maybe $3-5 per bulb).