planted tank

You can go either way. Mainly don't use aquarium gravel. Most of the plant specific substrates are well designed products with plants and their roots needs in mind. Yes they cost more but in the long run they are much better for the plants. I have used the gravel for 2 years + now and it has not broken down like most others do. I strongly suggest you purchase it.

 

so if i use plant substrate then i will be ok without covering it with sand

 

Yes definitely.

 

ok this sounds dumb in my head but i am going to ask it anyways i can use the same substrate in fresh and salt right

 

No way. Salt you need to use coral sand or aragonite. The substrates are completely different.

 

what kind of fertalizer do i use is Sw

 

If you have fish in the SW then you will not need fertilizer.

 

i will only have one pufferfish

 

That will most likely be plenty. You can feed it a little more heavily to increase nitrate and phosphates. You could probably fore go the use of a skimmer and chemical filtration media.

 

ill be ok doing that in SW????