Fishless Cycling Problem

Ok I think this is where I get confused. As I understand it if ammonia and nitrite stays at 0 for 7 days with no water changes then the tank is cycled? Is this the right way to think about it?

And after 7 days of zero readings, with no water changes being done, it means the tank is cycled for the amount of fish currently in the tank. It does not mean the tank is cycled for a tankful of fish as it would be with fishless cycling. This is why more fish should be added slowly.


Say you added the same amount of fish as you have at the moment. You'd have twice as many fish as you have now and they'd make twice as much ammonia as the fish you have now. But you'd have only enough bacteria to eat the ammonia made by the first batch of fish; you'd have to grow a lot more bacteria to eat the ammonia made by the new fish. You'd end up having to do water changes again while the bacteria grew.

The rule of thumb is that it is safe to add new fish that are  equal to a third of the fish already in the tank. The bacteria can grow enough bacteria for the new third quickly enough that ammonia and/or nitrite won't build up, and if they do appear it won't last long.
With 4 fish it is tricky to add a third of that number (one and a third fish) so the most I would add would be 2 new fish. You'd then have 6 fish. Then test the water again and when you've had zeros for a week, add more fish. A third of 6 fish is 2 fish, so you could add 2 more fish, making 8. Then test the water and when you have double zeros for a week, add 3 more fish, making 11. Then when you've had double zeros for a week, you can add 4 new fish, making 15 in total. A third of 15 is 5 so the next addition could be 5 fish. And so on till you have all your fish.

That's right.

Water changes - do them if you see ammonia and/or nitrite; and if you don't see any, once a week. Wth only a few fish you won't need to do a large weekly water change but you'll need to increase the amount changed as you get more fish till you are doing 30 to 40% once the tank is fully stocked.
Remember you have soft water with low KH so you'll need to do bigger water changes than most people just to keep the KH topped up. I have low KH too and with an overstocked tank I find that 40% a week is fine.

Re water changes, when I get to day 7, should I do small water change then before adding new fish?

That would be the logical time to do a water change. The fish already there will have settled in and you won't stress new fish by doing a water change shortly after they are put in the tank and haven't settled in yet.

That sounds good.
You could add fish later the same day if the timing is convenient for you.

I assume you want a shoaling fish that lives at the top of the water column like hatchet fish?

While they don't swim as high up as hatchetfish, how about golden/beckford's pencilfish Nannostomus beckfordi? Profiles here http://www.seriouslyfish.com/species/nannostomus-beckfordi/ and here http://www.thinkfish.co.uk/fish/golden-pencilfish.html They are about the same size as hatchetfish and pencilfish have an unusual way of hovering in the water which makes them an interesting addition to a tank.

To be honest it's a bit on the generous side. I prefer to stock to 80% of what it says I can have.

Since smaller fish tend to do better in shoals bigger than 6, your answer might be to have just 3 species rather than 4.

For instance,if you want fish that all come from the same part of the world, drop the Asian harlequins and get the south American neons, pencilfish and cories.

Bolivian Rams are pair forming... what stocking percentage would you be on with 2? Could you drop 1 of each of the others to make it work?  You'll get better more natural colouration and behaviour with a pair.

You need to be careful with getting a pair of rams, of either species - Bolivian or German/blue/gold/neon blue etc. These fish like to choose their own mate and getting any male and any female can end in a blood bath. And with Bolivian rams it is almost impossible to sex the juveniles in a shop tank. I know, been there, done that.

Several years ago I had a Rio 125 and knew nothing about rams neeeding to chose their own mates. I bought what I hoped was a pair of Bolivian rams which turned out to be 2 males. I was lucky because they did not behave as usual and they tolerated each other with only a small amount of bickering. Until the day I found a shop which had some adult Bolivian rams with their breeding tubes visible and I was able to chose 2 females. Once the males had something to fight over, they did and I had to remove one of the males to my quarantine tank within hours. The remaining male paired up with one of the females, and they both attacked the second female. Luckily the shop bought back the spare rams.

If you definitely want rams watch the shop tank quietly for some time. Once they get used to you standing there they'll go back to their not-being-watched behaviour. Some of the fish will chase other fish away. Those are males. Some of the males might allow one other fish near - these are females that the male likes and are most likely to pair up with. Buy one of the males that allows another fish near, and the fish he allows near. I would take someone with you to go for an assistant while you keep an eye on your chosen fish.



Or get apistogrammas instead. A 1 male 2 female trio is do-able in a Rio 125 - I've done that too. The most common apistos in shops are cacatuoides (cockatoo cichlid) and agassizi, both in a few colour variations.

Looking on Fishbase (the site written for scientists) the temp ranges of the fish on your list are:
harlequins - 22 to 25^oC
panda cories - 20 to 25
cardinal tetras - 23 to 27
neon tetras - 20 to 26

Neons would be a better match for panda cories and harlquins with a temp 23 deg C.
The 1 deg rise when the lights are on won't do any harm but I would turn the heater down to get 23 with the lights off and 24 with them on, or even 22 with lights off and 23 with them on.