the reccomendation is 1" per gallon (excluding tail), with a maximum of 2" per gallon after 6months.
But fish size is important too.
6 x 1" fish will produce less waste than 1 x 6" fish!
in the rekord 800 i wouldnt go above 6 inches anyway, otherwise they dont have enough swimming room.
You also need to decide how to cycle your tank, there is numerous ways:
1) get some "mature" media (media that already has bacteria on it) and add it to your filter to get an 'instantly' cycled tank. ask a friend or LFS
2) silent cycle. This method is the main one carried out on here, it is where you fill your tank with lots of fast growing 'weeds' and cover 75% substrate, and stock lightly. This is so no dangerous ammonia builds up and kills you fish. The plants help to use the ammonia as a nutrient too. You can do daily water changes, or 2 x 50% a week.
3) fish in cycle. This is where you stock lightly, and perform frequent water changes to keep the ammonia levels down, similar to the silent cycle except you have no plants to use the ammonia. Most people are against this method as it puts your fish most at risk
4) fishless cycle. This is where you add 5ppm everyday, until the bacteria colonizes,
all methods take about 4-8wks to become fully cycled.
Dont buy anything such as nutrafin "cycle" which supposedly contain the beneficial bacteria - they dont!
LFS will most likley to advise you on a fish in cycle.
more info:
http://www.fishforums.net/index.php?showtopic=277264
