The Aquarium size, depends of course, of the size of the species, you want to keep. In our opinion, the ideal Aquarium size for Brackwater Puffer Fish, should have a minimum volume of 160litres. In this, you can easily keep, Tetraodon biocellus or other Juveniles of other species until they reach about 5-6 cms TL. Depending on how aggressive they are, you can keep a single fish or several. There isn't rule on how many you can have, but it is recommended that you have the biggest Aquarium possible.
The Technology of a Brackwater Aquarium should not necessarily be any different to the Fresh Water Aquarium. Although the stocking rate and the Salt level is important.
The Filter Technology of the Fresh Water can be used, where you can choose between Internal and External filters or Hmf (Hamburger Mattenfilter= Hamburgish Mat-filter) It is up to you which one you prefer. From our experiences, all Types of filters work well with the Brackwater. Attention!! External Filters, with integrated Heaters, are not advisable for Brackwater! Filters that are said, to be not good enough for Sea water, are also not recommended for the half salty medium. The usage of an extra Flow Pump is advisable, as the main Filter only omits little flow.
Also the usage of a Diffuser, or a good source of Oxygen is important, as the Brackwater puffer fish (as all Puffer fish) are Oxygen dependant animals. A good water surface movement should also take place. You should not be alarmed by a good algae growth; Algae are unavoidable in Brackwater and even welcomed!
If stocking and salt levels are higher, you should think about a skimmer and possibly a Nitrate filter. Puffer fish have a high metabolism, and frequent water changes could possibly make you very poor. A skimmer works from a density of approx. 1,012 reliably, and from 1,015 stable. It helps immensely, to keep the water quality high and also gives a good oxygen supply. Higher N03 counts in Brackwater are not so dramatic compared to freshwater. But if u keep several large Puffer fish, the Filters can turn into Nitrate catapults, this is where it could be useful to use a Sulphur filter for the reduction of Nitrates.