First off.. best time to put any fish in a tank? When Ammonia and Nitrite are at acceptable levels (I.e. 0ppm). Invest in some test kits or ask if you LFS will test your water for you. Once everything is gone in terms of Ammonia, Nitrite and majority of Nitrate, then it's time to add fish!
To create a Biotope for Figure of 8 Puffers is fairly easy! Sand as substrate is a definate. However, with my Brackish tank I also brought a very small bag of natural looking gravel and scattered it over the sand just to break it up and not look all sandy! Also, areas of just gravel will do no harm!
Rocks are important too! Think estuary water when planning for a figure 8.. wide open spaces, so some bigger rocks and smaller rocks will do too! Try not the use up too much swimming space though - just enough to provide some cover (espically with more than one Figure of 8 Puffer!) As for plants it's hard to find real plants that will tolerate the salinty levels in a Brackish tank. Vallis is the most likely to survive but I tend to go with the silk alternative. These are artifical plants but look very realistic espically if you buy a good brand and most LFS stock them so they should be easy enough to find!
98 Lites is over just over 21 UK Gallons (Roughly 26US Gallons) so don't go too mad with stocking as the Figure of 8's will appreicate the swimming space. I would only add 2 in a tank this size, purely on swimming space alone. They are fairly aggressive towards their own kind so 2 is a good number.
Also, remember to flucuate the salt levels as would happen in an estuary. Try to mix salt between 1.004SG and 1.010SG just to try and re-create the natural Figure 8 environment.
this isn't exactly what you are looking for in terms of a biotope, but it's not too far off!
Further reading for ya:
Here
Here
And Here!
Hope this helps
TIMMYSTOOD
