Ahhh, the lunar perigee (the super moon) due tomorrow. OH has been banging on about this for ages but pic from the last event, 1992 was it (?) here - it's certainly big! He is out photographing as I type!
As for stocking, a lot of people I'm sure will use their own basis. Not sure how long your tank has been set up for but newer tanks need less stock than mature tanks of course as filters catch up and the tank generally 'settles' to provide natural food that some fish need.
The maturity of the tank, usually classed as 12 months in min) will have an effect on comments below. In mature tanks you can sometime get away with adding ?a few more?.
I?d agree with Noodle here on initial stock though
To start with most people tend to stick to a very rough calculation of 2.5cm of fish per 4.5 litres of water. This is based on the adult size of the fish. TBH though, it's rather antiquated now, as stock will be driven by a number of factors including filters (the upgrading of) and water change regime. Also this old formula doesn't work with any fish bigger than 5-6cm really as you have (as these need more swimming room and create much more waste) but it?s certainly useful as a starting off point with smaller fish.
If keeping small shoaling fish, FK generally recommends stocking 6 fish first, waiting a month to ensure filter catch up and all is well, then adding further fish spaced similarly apart, ongoing.
After that, stocking tends to be related to several factors, i.e. weekly water params ? are all levels good?, how fast does nitrate increase each week in between the water changes (if it goes up by more than 10ppm, that can be an indication of overstocking) but just generally allowing the fish lot?s of space and room. How often do you like getting the buckets out LOL?
120 litres tank - 10% for substrate/decor = 108 litres water
Existing stock have maximum adult sizes as follows:
Gold Spotted Plec = 30cm Rainbows x 2 = 28cm Cardinal Tetra x 9 = 45cm Total: 103 cm of adult stock
Existing Tank suits: 108/4.5 = 24 24 x 2.5cm Total: 60 cm of fish length in total.
A number of variables apply though as stated above, depending on maturity of tank.
You can play around with these figures/stats of course, depending on what you decide to re-home or perhaps have as new stock. To be safe, if you decide to rehome the bigger fish, just apply the above formula when stocking with the smaller fish you favour to ensure the tank can cope and the fish have enough room initially.
As an easy reference (I use this too!), 6 small shoaling fish (5cm max) per every 60 litres is usually a good bench mark to start with, gives them room and easy water changes for the keeper in a newish tank! Hope that helps
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