Thanks Chasmodes! I hope to see your oyster reef come alive some day. Your local, Maryland biotope idea is unique, and I think it will turn out to be beautiful!
I hope the info is useful. Seeing people spend good money on new lighting in attempts to save their macros is a little frustrating. Most of the time, when macros crash, it's not because the lighting is the wrong color temperature, it's because they are starved of a particular nutrient. And there's really only a few to keep up with, so it's pretty simple.
My number one recommendation to the vast majority of macro keepers is this: buy a simple CO2 regulator for less than a hundred bucks. Remember the C-N-P ratio: 300-30-1. Carbon is the big one-300! Most macro keepers do absolutely nothing to supply carbon, other than adding fish food. The most important nutrient to these plants is completely ignored! You cannot expect success if you ignore the most important ingredient.
Nitrogen is the second most important nutrient for plants. As an aquarium matures, the resident bacteria becomes very efficient at consuming nitrogen, in the form of ammonia, nitrite and nitrate. This is great for the fish, but not for the plants. In mature tanks, bacteria outcompete plants for nitrogen. So you need to dose it. Plants' preferred form of nitrogen is ammonia, but ammonia is rather poisonous and dangerous. So, a safer-for-aquariums form of nitrogen is needed. As we all know from our lessons on cycling, nitrite is also harmful to fish, etcetera, so that leaves us with good old nitrate-harmless to fish, and food for plants. Potassium nitrate is readily available at hardware stores.
If you have fish, and you feed them, you are already suppling enough phosphate, so nothing is required. If you have no fish, you will need to dose phosphate. The easiest way to do that is to simply add fish food to the tank. You'll have enough phosphate for the plants, and you'll be feeding the bottom of the food chain as well.
The only thing left, is trace elements. Some are added with fish food. Some are replenished with water changes. Buy a simple trace elements supplement in a bottle.
And that's it. Simple.