When Can I Add More Fish?

First of all, a couple of definitions.

Shoaling fish are those species that in the wild live in groups of hundreds, if not thousands.
Schooling fish are those shoaling fish that always swim together in a group.

Non-schooling, shoaling fish do not stick together in a group in the tank unless they are stressed or afraid.
Shoaling fish, both schooling and non-schooling, need to be kept in groups of the same species. If there aren't enough of them, they become stressed by the lack of numbers. It is usually reckoned that they lose count around six, which is why that is the minimum number you should have in a shoal. Though some people reckon they can count higher than six, and the shoal should be bigger.
Fish of similar species will stick together when forced to by lack of their own species, eg your zebra and pearl danios, but they are much happier in groups of their own species - even if they do not school and all go their separate ways in a tank, they know there are others nearby to school with if something threatens.



When doing a fishless cycle dosing to 3 to 4 ppm ammonia, you should be able to get about two thirds of your final socking list as soon as the cycle has finished. The fish to leave till later will include species that need a mature tank (one that has been running trouble free for 6 months).
Using the community creator (I have assumed your tank is 80cm long because that's what mine is  ) you are currently 22% stocked. Increasing the four species to six each pushes you up to 45%.
You have room for some bottom dwellers eg one of the dwarf species of corydoras (pygmaeus, habrosus and hastatus, though only habrosus are in the fish profiles on here) and perhaps a centrepiece fish.

Whichever fish you decide on there are a couple of points to note.
You need to get them within a few days or the bacteria you spent a while growing will start to die off as you don't have enough fish at the moment to provide enough ammonia.
The danios like the temperature a bit cooler than most tropical fish. I would look at fish that can live happily at 23 to 24 deg C, and set your heater for that temp.
Do you know if you have hard or soft water? That info should be somewhere on your water company's website. Fish will be healthier if you choose those that prefer your hardness - hardness is more important than pH.


One other thing - for testing pH, run a glass of water and test it straight away. Then leave it to stand for 24 hours and test again. You'll probably find they are different. The pH after standing is the one to work with.

Once you stop feeding the bacteria the amount of ammonia you used to cycle with, they will die off slowly. The amount of fish you have now won't provide the 3-4ppm you were using. But you say you only got these fish very recently so the bacteria will only just have begun to die off. It will take several days for them to die off to just the amount needed for your current fish. If you get more within 2 or 3 days, you'll be OK.
A lot of people do say you can get all your fish at once, but I prefer to get a bit less than that. This gives you some wriggle room if things should go a bit wrong.

If I were you, I would increase my shoals of the fish I have as soon as possible. The harlequins and glowlight danio really do need to be in a group of six each. Since the danios are so similar, you could get away with 4 each rather than fill your tank with similar looking fish. Once you had about 20 fish, you could stop there till you decide on what else. Yes, your bacteria would reduce in number but once you do know what you want next, so long as you take it slowly you'd be OK. If you made the numbers up to 20 asap, you'd be safe to add new fish the same size as six of the fish already there - six fish the same size or three fish twice the size etc.


Your water is moderately hard. This means that you only need to avoid those fish which must have very soft water or very hard water - no Rift Lake cichlids for example. If you read up on the fish you like you should find out if they need one of the extremes of hardness.

Thanks again Sue, that makes a lot of sense. I have already informed my 7 year old that we can go fish shopping again today 
Do you have any thoughts about a bottom dweller?

Corydoras catfish are my favourite, but you should have at least six of those for them to be happy. The only cory cats on this web-site are one of the three dwarf species and the Panda cory (link) so you'll have to look elsewhere for info on the others. Bronze corys (link) are the most common, but you'll need to see what the shop has and what temperature range you want. Panda corys require cooler water than most others.

You said 'a' bottom dweller, so if you only want one then the bristlenose plec (link) would be my choice, as long as you have some bog-wood in your tank for him/her to chew on.

Colin, the thing that worries me about cories in suep's tank is her sharp gravel........

Here's a very different view of the 'sharp gravel' argument...... Clickety click.


....and here's a small extract:

This particular myth has been around almost as long as I've been keeping fish, and it refuses to die.
 
One of my favorite test tanks used crushed glass substrate (not kiln-softened) and a school of C. arcuatus corys (personal favorites) with fractured glass slab "rockwork". A part of the same shipment of corys went into a nearby planted tank with which I had been having problems with a high-organic substrate. After just a few months, guess which tank had barbel erosion? And a few weeks after unifying the schools, guess who started recoving their injured barbels while living over crushed glass?

HI Sue & Colin
Thanks for the replies. I have been to 2 different LFS's today (and done some miles!) But neither had any glowlight danios  I have added 2 more harlequin rasboras and another pearl and zebra danio (I did understand you Sue 
One of the shops which has won awards for aqaurium standards had a cory in gravel just like mine. He said it was fine! However, I took a water sample for them to test the nitrate level as I felt it 40-80ppm was far too high (despite 2 large water changes 50% then 30%- tap water is 10ppm). Neither shop would test the water and both said that nitrate levels were not a problem for the fish. The only consequence was an algae problem. Mind you, neither seemed very impressed when I said I had done a fishless cycle! The tank is well planted but I guess it will take some time for the plants to affect the nitrate levels. I can't understand why the water change had no effect on the levels? I didn't want to change too much because of getting rid of too much bacteria.

Very few shops approve of fishless cycling 

Ain't that the truth.  When I started out the reaction I got from one was "You're doing a WHAT?!?", the other said "Oh dear, that's going to take you forever." - Glad I did the fishless cycle though, it was worth the extra effort, and time.

I didn't want to change too much [water] because of getting rid of too much bacteria.

There are very few bacteria in the water itself.  They want to live attached to things, so they will be on the substrate and plants and glass etc.  However, the vast majority of the bacteria live inside your filter.  For all realistic purposes you can forget about the ones that don't.  So you can do as large a water change as you wish.

 
Thanks guys, The fish all seem fine except one zebra danio I added yesterday who keeps hiding - not sure if he just needs to settle in or he is ill. Will keep an eye on him. You're right Resa - I do value this site beyond any LFS and I'm soooo glad I found it!!

Thanks Colin
There is one more LFS I can try which is difficult to go to as there is no local parking near it, but I think you're right. 3rd time lucky eh!?