Luck, Skill Or Should I Be Worried?

Hi everyone, a bit of background, I kept fish all the time I was growing up, years I had tanks running but then life got in the way but now I've settled down it was time to invest again.
I have a 120lt 90cm tank with an oversized internal filter box, the tank has been running approx 3 weeks, 1 week empty, 2 weeks with fish (6black neon tetras) I have 4 small plants (apologies but I know not what they are), 2 lumps of bogwood and 4 medium pebbles (off Brighton beach), everything was boiled for about an hour before placing.
I have approx 60% gravel and 40% sand ( I've always loved Julii corys so planned for them with the sand).
Now you have an idea of my tank I get to the confusing bit, nothing is happening, or it appears nothing is happening with the cycle, I added a bacteria booster when I added the fish and test the water twice a day (morning and evening) nothing is showing up, no ammonia, no nitrites and only slightly more nitrates than the base I get out of the tap. I've even bought 3 different testers to factor out getting a duff batch still no results whatsoever, not once.
Anybody have an idea what's going on? I'm at a loss and wondering if I should be concerned, any help anyone can give would be amazing.

Hello Adam, and welcome to the forum.

Yup - just keep testing and don't be tempted to add any more fish for a while yet. Patience you must   

If you are not getting any reading above zero for ammonia and nitrite you can do water changes less often. 6 black neons in 120 litres aren't going to make very much ammonia at all. Try dropping your water changes to once a week, keeping a daily eye on those levels. If you haven't seen as much as a blip in for the next couple of weeks, you could get a few more fish - maybe equal to 3 black neons - and watch those levels daily again. If you see ammonia and/or nitrite, do water changes to lower them.

Oohh missed the bit about mts 

I would hold off those a couple of weeks as well. 2 would be a good number. They will breed quite happily and if you overfeed the fish you'll end up with hundreds 

then maybe a loach!

Just to warn you, loaches need to be in shoals of at least 4 with more being better. And there aren't many that will fit in a 90cm tank, dwarf chain loaches being the only one I can think of.

Kuhli loaches also need to be in a group, very unhappy on their own, so don't buy "a loach". They also need places to hide and enough sand to bury themselves.

Here's a pic of my little habitat, if anyone's interested!

Not sure if kuhlis, corys AND bristlenose wouldn't be a bit over the top for bottom fish. There could be conflicts.

The only realistic way to lower hardness is with RO water I'm afraid. Either mix it with your tapwater to get the hardness you want or use just RO with added remineralisation salts.

As for losing your sand, do you siphon the tank water into a bucket or down the sink/out of the window with a hose? If it's into a bucket, carefully pour the water away and wash the sand with tapwater then put it back in the tank. The tiny bit of chlorine with the sand won't do any harm. That's what I do.

I use rain water from a water butt to dilute my liquid chalk. It's OK as long as the level in the butt doesn't get too far down.... and then I use RO. I wash out the gunk from the bottom of the butt once a year - which reminds me.... it's that time of the year again.