A little in defense of the volume per length calculators its not a bad way of toting up, IMO its so unaccurate both ways you can determine some kind of guide as to how well it will work.
In this tank I would probably look at upping some numbers that you already have, especially some of the cichlids you have. When I saw you mention a Geophagus and started reading your list I instantly thought of their smaller cousin the Cupid Cichlid, but then I saw you already have - I would really recommend getting some more of them as they are a gregarious cichlid and in a tank that size you can totally get away with a nice group of them, and they will do the same job as a Geophagus especially as they grow.
I would also up your Apistos with an other female just to give your first a break from the male now and again as she will need it.
I kind of feel that you are trying 2 set ups here, you have a nice array of dwarfs in there but then you add in stuff like your Sheatfish and want to add Pictus and Geos. I mean since the issue was raised about you adding Pictus the same can be said for the Sheatfish which after a quick google reveal a gorgeous fish which grow to 8 inches and eat smaller fish
see what Im saying?
Also with the Knight Goby, generally considered a brackish fish
And similarly I dont feel the requirements of the Rams are being met either. They can be a delicate fish, especially the newly line bred Electric Blues, as stunning as they are I would be more tempted to keep them in a tank dedicated to them specifically with a low Ph and high temperatures. Not sure on what your Ph is but while you have fish like the Barbs and the Gourami (among others) in there its not going to happen with regards the temperature as they will not be able to cope long term with it. What is often found with Rams in these conditions is that they waste away after about 18 months where as they should live to about 5 years. This is because the low temperature messes with their metabolism and in turn can effect their gill function. For this reason I would always recommend Bolivian Rams for this kind of set up....
For me, I would stick with the dwarf and smaller fish in this tank, though odds are the Denisons would be a welcome addition to this kind of set up. But in doing so I would split your rams from the main tank into a tank of around 20 gallons or more and keep them as they will thrive with a high Ph and consider lowering the Ph naturally (if your Ph is not already low) with Almond Leaves.
As much as I hate to say this to people but I would seriously consider rehoming the Sheetfish as I really do think they will pose a threat to your other fish in later life.
So for me I would have in the 300liter
3 Cockatoo Cichlids (1M, 2F)
5 Cupid Cichlids (mix of genders)
3 Dwarf Gourami (1M, 2F)
5 denisonii barbs
5 celebe rainbows
9 fork tail rainbows
1 bristlenose
1 amano shrimp,1 bamboo shrimp (perhaps up your shrimps if you want to, I would probably recommend it)
And then yeah you probably can add more to the tank quite easily just think smaller, more general community fish rather than things with requirements or brackish water etc etc. Personally I think Loaches would work really well in this tank and a nice big group of Dwarf Chain Loaches would be brilliant!
Then moving the Rams over to a 90 liter (or larger) I would probably look to do something like
3x Rams - 2 German Blue 1 Electric Blue
8x Rummy Nose Tetras
8x Sterbai Cories
And like I say in there a higher temperature and a low ph will be perfect, adding the Almond leaves is the best way to go as it lowers it naturally and it will calmly lower your tap water down to around 6.5/6.8 depending on how many you use per liter/gallon.
Hope thats helped, it is intended to and not to offend but I can see you kind of hitting problems in the future for a number of different reasons so really wanted to flag them now before things get out of hand.
Wills
