Leaves going yellow then transparent - help!

We need more information.
What kind of substrate and how deep, what lighting, what size aquarium, what method of CO2.
the thing with plants is that every single component must be taken into account to understand what is going on.

Ok - using Fluval Stratum substrate and the default full spectrum 30W 6500 light fixture. The tank is the Fluval Flora and I"m injecting CO2 via a tank.

what kind of light, is it a t5, t8, t12, led?
and what size tank
the type of light is more important than the amount of power the light is using to generate light

With CO2 injection, I suspect all nutrient's are lacking independent of any lighting, other than possibly single T8.
I might look to Aquariumfertilizer.com. or Greenleafaquariums.com for macro-micro nutrient package.
At very least,,I would maybe add Flourish Comprehensive plant supplement twice a week.
Might also look into Estimative index dosing for planted aquariums.

It's a T5 lighting. The tank size is 8 gallons.

oh yah, thats definitely a nutrient deficiency. I assume you are running a high tech tank so you should be doing EI dosing (although idk how to dose such a small tank)
There is a user here, nicolig or something like that (wow I'm bad with user names lol) that sells dry ferts for cheaper than most websites I've seen. He also helped me figure out exactly what I needed. He should have a sale thread in the Swap place.

Hmm...would Seachem's Flourish Comprehensive supplement be enough?

No, you need a proper balance. If I am understanding your set up correctly, you have high lighting and pressurized co2, both of which encourage plant growth. However, you are missing macro and micro nutrients, which are the the fuel of growth.

Right now, your plants are probably getting all the signals that tell them to go wild but they are not getting the means to do so. I would look into EI dosing, buy dry ferts, and do that. It seems annoying and difficult but trust me, its not. I managed to figure it out and I'm not always Mr. Intelligent with these things lol. Dry ferts are also cheaper than buying liquid ferts and its the same thing.
Really, with proper fertilization your plants will be booming in your type of setup, and I'd be willing to bet that you could keep almost anything you'd want.

Check out nilocg's latest thread from yesterday: http://www.plantedtank.net/forums/showthread.php?t=188066

Here is a good link for EI Dosing: http://www.plantedtank.net/forums/showthread.php?t=21944

For a tank that size, I'd recommend liquid dosing of EI - much easier to measure. I see that you're in Canada - that might be a problem for KNO3 (or one of the common ferts).

There is an alternative chemical to KNO3 that you can get across borders.
Nilocg was very good to me, so I'd recommend buying from him as well and asking his advice.

Darn....I wished I was back in school - chemistry classes: I'd have full access to all the elements to make a soup

Thanks for the links and the wealth of information everyone.