Freshwater Puffer tankmates

Alright, I've officially fallen in love with my 'snail irradication submarine' (aka juvie spotted puffer) - so I'm NOT going to give him to my friend afterall. I have found that if I put him with female bettas - he either goes after them or vice-versa. So mixing him with the 'girls' is not an option. He did seem to mix well with the ghost shrimp - as long as his tummy was full of easier to catch prey like pond snails and/or shrimp pellets.

So I'm eyeballing an empty 29T. I've got a great spot in the classroom to make an 'estuary' model. Basically, it'll be filled with 'grass-type' aquatic plants and slightly brackish. I'd like to mix things like mussels and shrimps with him. What other slightly brackish water fish would go well with this puffer?

In my experience puffers did best with other puffers they tend to get pretty aggressive