General Brackish Problems

Leave the light on for 8-10 hours. Your plants are probably dying because they do not have enough light and the algae is out-competing them for nutrients. Use Flourish Excel plant supplement.

Give your puffer something to explore. I would be bored to if I didn't have anything to do. Caves, tunnels, bubble wands...whatever.

Change your puffer's diet. You need to feed it snails to wear down its teeth, if you don't, the teeth will eventually grow so long your puffer may not be able to eat. Then you will have to trim its teeth. You can give your puffer bloodworms, mysis shrimp, clam...there are tons of options. Would you want to eat the same thing every day? It's boring and it's not healthy, your puffer may be missing out on nutrients he could be getting from different foods.

Go and check out this site www.thepufferforum.com

Here are two pictures of my 29 gallon F8 tank.
I usually re-arrange once a month to keep them from getting bored.

You can't add any more fish to this tank as it is fully stocked with the figure 8. You could look into some brackish plants. Here's a sticky on www.thepufferforum.com with discussion and a link to a list of brackish plants.

You can also use a variety of plastic or silk plants if you are concerned about the plants dying. Growing brackish plants can be tricky since many plants cannot live with the salt and pH of brackish tanks, and many times the plants that can live in brackish are grown and sold in freshwater and need to be slowly acclimated to brackish.

I'm surprised that your puffer is taking the pellets at all. You really, really, really need to get him on a more appropriate diet. He needs crunchy and meaty foods like live snails and shrimp and frozen foods (properly thawed before offering) like shrimp, mussel, clams, squid, krill (only feed occasionally, not a good regular diet as poor nutrition and can cause lockjaw in certain puffers like Figure 8s when fed regularly), earthworms, etc. Their diet can be supplemented with foods like spirulina brine shrimp (or brine shrimp soaked in vitamin solution), bloodworms, mysis shrimp, glassworms, etc.

With his current diet, he will have tooth overgrowth, poor nutrition, and boredom. I assure you that you both will be happier with a good diet for him. I say you because you really don't want to have to trim a puffer's teeth manually. The first time I did it (was feeding a decent diet but with only rare snails), I was shaking so bad from nerves that I could not trim his teeth and had to try again a week later.