Weird fishless cycle

[TreeDimensional]

I am attempting a fishless cycle in my first ever aquarium (a 20g, Superfish Scaper 90). Currently on day 6 and things aren't what I was expecting. Here's how it's gone so far:

Day 1: Set up, add substrate/rocks/wood, add water + Prime, leave running overnight

Day 2: Measured baseline parameters and added Stability (and have done every day since).
pH: 7.4-7.6 (both normal and high-range were at the limit so I assume it's inbetween)
Ammonia: 0.25-0.5
Nitrite: 0
Nitrate: 20

Day 3: Added plants and a small pinch of fish food
Ammonia: 0.25-0.5
Nitrite: 0.25-0.5
Nitrate: 40

Day 4: Dosed ammonia up to 4ppm
Ammonia: 4
Nitrite: 0.5
Nitrate: 80

Day 5:
Ammonia: 2
Nitrite: 0.5
Nitrate: 160

Day 6 (today): Did a 50% water change to reduce Nitrates as I heard too high can stall the cycle
Ammonia: 1 (before w.c.), 0.25-0.5 (after w.c.)
Nitrite: 2/0.5
Nitrate: 160/80-160

I have just added ammonia back up to 4 and will continue to measure until it can get to 0 within 24 hours along with the nitrites.

So here are my observations/unexpected behaviour:

1) Ammonia has gone down a lot quicker than I was expecting. Everything I've read/watched has suggested this is a slow process, but I went from a strong 4.0 on day 4 to 2.0 on day 5. I haven't got any previously used filter media or anything, so my only assumption is either the Stability is really going at it, or the plants I bought from the shop have brought some bacteria over?

2) Nitrates are really quite high, is this something to worry about?

3) I thought things would happen in a linear progression (Ammonia -> nitrites -> nitrates) all in a measurable manner, but it seems a bit haywire. Does anyone else have experience similar to this?

I suppose I'm just looking for some reassurance that I'm on the right track. A few snails hitchiked along with the plants, but they seem to be faring everything pretty well.

 

[Aiken Drum]

What you are seeing isnt what you would expect to see, but it is what people often see.

Ill start off with a bit of speculation on why your ammonia is going down quicker than you are expecting.

There are numerous types of denitrifying bacteria that will convert ammonia to nitrate. Some are great at doing this short term, but dont multiply well and dont establish in your filter media. What im seeing being said is that many of the bottled bacteria products are of a type of bacteria that are like this, you see great results for a week, then you tend to see a backward step in the amount of ammonia being processed because the bacteria isnt good at establishing in your tank and just dies off or gets removed as you change water. You could be seeing the first part of this, but hopefully not. See how things progress over the next week or 2.

Another thing to take account of is your test kit is a home test kit, not laboratory testing. It wont be all that accurate and all sorts of things in the water can cause false results. Nitrate in particular is difficult to test for, even in a laboratory. 2 things that are often cited as causing false high nitrate readings are nitrite and water conditioners. Seachem will tell you that Prime can cause false high results for nitrate with the API liquid nitrate test (although that could just be them trying to get you to buy their test kits).

You have been throwing all sorts of chemicals in the tank, new substrates, decorations etc. So a few anomalous readings are to be expected.

Honestly, just dose your ammonia to 2ppm, when your ammonia is gone redose and start testing for nitrite too. Dont even bother testing for nitrate until you are seeing zero ammonia and nitrite in your daily testing after dosing 2ppm. Just so you know how much of a water change you need to bring nitrate down before adding fish. It just confuses things when you see results you arent expecting. The only time i would consider a water change during a fishless cycle would be if nitrite got to a level off the chart.

What are your plans for the tank? Hope you keep us informed of progress.

 

[TreeDimensional]

What you are seeing isnt what you would expect to see, but it is what people often see.

Ill start off with a bit of speculation on why your ammonia is going down quicker than you are expecting.

There are numerous types of denitrifying bacteria that will convert ammonia to nitrate. Some are great at doing this short term, but dont multiply well and dont establish in your filter media. What im seeing being said is that many of the bottled bacteria products are of a type of bacteria that are like this, you see great results for a week, then you tend to see a backward step in the amount of ammonia being processed because the bacteria isnt good at establishing in your tank and just dies off or gets removed as you change water. You could be seeing the first part of this, but hopefully not. See how things progress over the next week or 2.

Another thing to take account of is your test kit is a home test kit, not laboratory testing. It wont be all that accurate and all sorts of things in the water can cause false results. Nitrate in particular is difficult to test for, even in a laboratory. 2 things that are often citing as causing false high nitrate trading are nitrite and water conditioners. Seachem will tell you that Prime can cause false high results for nitrate with the API liquid nitrate test (although that could just be them trying to get you to buy their test kits).

You have been throwing all sorts of chemicals in the tank, new substrates, decorations etc. So a few anomalous readings are to be expected.

Honestly, just dose your ammonia to 2ppm, when your ammonia is gone redose and start testing for nitrite too. Dont even bother testing for nitrate until you are seeing zero ammonia and nitrite in your daily testing after dosing 2ppm. Just so you know how much of a water change you need to bring nitrate down before adding fish. It just confuses things when you see results you arent expecting. The only time i would consider a water change during a fishless cycle would be if nitrite got to a level off the chart.

What are your plans for the tank? Hope you keep us informed of progress.

Thank you, your post is reassuring. I'll just keep it simple in that case and do as you say. As for stocking plans, I'm not set on anything yet. My partner and I have been to a few shops and we've made a list of fish we like the look of:
Red Lip Goby
Albino Cherry Barb
Red Rilli Shrimp
Cardinal Tetra
Lampeye
Bristlenose Catfish
Khuli Loach
Snakeskin Red Delta (and basically all guppys)
Blind Cavefish
Dwarf Gourami

Closer to the time we'll do some deep research into which of these species are appropriate and which ones are compatible with each other. Personally I really like all kinds of loaches, and my partner likes shrimp but some quick googling has shown that loaches will eat shrimp?

I think we'll probably start with some guppys before adding anything else.

The hitchhiking snails are, as far as I can tell, juvenile Ramshorns and Malaysian Trumpet Snails. They seem pretty hard as they've survived things so far.