Fishless Cycle

I didn't know that, Matt.
Like termites rely on microbes in their gut to digest cellulose in wood. I remember from biology that if you heat a termite to a certain temperature it doesn't kill the termite but it does kill the microbes and then the termite starves to death

I use a filter intake sponge on my canister filter.  Not only does it protect your fishies it also acts as a pre-filter so the canister filter material doesn't get dirty as quickly or get blocked by large bits in the hose.  I have a quarantine tank and if I need it at any point I'll replace the filter intake sponge with a new one and use the good bacteria from the old one in the quarantine filter.

If you haven't already cleaned the filter media, I would see what it is like. When dirty, they are usually covered with brown goo which needs to be gently washed off. With a new filter you need to be extra gentle as the biofilm won't be completely bedded in yet. Squeeze sponges in a bit of tank water that you've removed from the tank, and swoosh any ceramic media.

If the particles are very fine, adding some filter wool (aka filter floss) might help trap them as they are too small to be trapped by a sponge. You can buy rolls of it or a length cut off a roll. Shops that also sell pond supplies are more likely to sell it like this.
Filter wool doesn't wash well as it goes into holes very easily but as it is not a very good home for the bacteria it can be changed regularly with out affecting the bacteria colonies.

You can do it with a water change of any size because there are virtually no filter bacteria in the water so it won't cause any problems.

Provided you remember to dechlorinate the new water and use warmed water 

The bacteria we want live attached to surfaces. They live in the biofilm which covers all the surfaces in the tank. Filter media is designed to have a huge surface area (think of the surface of all those bubbles in sponges) which is one reason bacteria like it in there. The media is also in the dark and has lots of food and oxygen laden water passing through, which encourage the filter bacteria to grow in there.
In a brand new cycling tank the biofilm is still forming which is why you need to be gentle cleaning the media.

The brown gunge does not contain many bacteria, it is mainly organic waste - when you have fish, their poo, uneaten food and bits of dead plant break down to make this gunge. However, there is possibly some biofilm forming on the bits in the gunge.

Next time you open the filter I would be inclined to pour away the dirty water but don't wash the casing of the filter as there will be biofilm growing on that. Plenty of time to rinse the casing once the tank is cycled.

Just thought I'd give an update....unsure if anybody is overly interested, but everyday something is learned.

So a couple of weeks ago I upped my co2. Started to get foam in the corner of the tank. It took my child who looked up, the honey gourami have laid eggs as of yesterday, and he was preparing, I also didn't know who the fiend was tearing up a buy of plant life!

The male is chasing everything, even the female. I don't hold out much hope as I don't have another tank, and I'm going away for 10 days.

I have a fish feeder, under strict instruction, my mother, and have just done a big change, hence another reason for the gourami to feel upset. She can top up dechloribated but not a water change. I think I'll be fine overall.

Regards

Hi Sue I do top up - I'm using fluval aqua plus water conditioner everytime no matter how little or much (in the doses recommended). I've only ever used treated tap water, is this wrong ?

What's pure water?

Ok, all my readings looked good including ph. I thought the treatment did the job. Do I buy in certain volumes and store at home? Is this just for topping up?

Just to make things clearer - plain RO or deionised water is just for top ups between water changes. Weekly water changes still need to be done, and these can use tap water as you remove as many minerals as you put in.

By plain RO I mean RO water as it is made, and that the shop has not added anything to it.