Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
It sometimes helps if you limit the number of distinct questions you ask at one time. If someone doesn't know the answer to the first one, they tend to immediately move on; or if they see a reply, they may assume it's answered all the questions rather than just one.
You have three questions in this thread:
1) Skeletonized swords. I don't know the answer to that one. Although it could indeed be a combination of the factors you've listed (high light, not enough CO2, plecos).
2) CO2. You can get adequately high and stable CO2 levels from DIY on a 30G high, but it takes multiple bottles, and you have to replace mixtures on schedule. Pressurized is easier once you get it set up. I pieced together my pressurized system from a variety of sources, so I can't recommend a simple, ready-to-use system. Regardless, you should immediately invest in a drop checker and 4°KH solution, which tells you your CO2 level regardless of DIY or pressurized. Your current airstone diffuser is probably quite inefficient.
3) Dead fish. Do you have an ammonia and nitrite test kit to test for these toxins, which could accumulate if the biofilter isn't fully cycled, isn't working properly, or there's a dead fish rotting in a hidden location that produces more than the biofilter can handle? Are you using tapwater for water changes, and a dechlorinator that is effective against both chlorine and chloramine? Are fish showing any signs of disease, or unusual behavior, prior to death?