Think Fish Keepers Daily News. [2016-2019]

@Sue and a new skill. I will be watching out for reports of 'bank jobs' with a neat hole cut in the window, vault empty, the tank in the bank managers office nicely siphoned and the fish fed.

I possess some skills/traits/mannerisms of my grandfather who died the year before I was born, but which skipped a generation, so it's altogether possible that glass-cutting is a genetic skill in your family line, @Sue.

Over the course of 24 hours, my nerite snail managed to cover about half of the substrate in poo. I wasn't able to get a water change done until a few days later, by which time the nitrates had gone up from their usual <20ppm up to 40-50ppm for the first time ever! No wonder he was found perching on dry land yesterday, on the very top of the heater. His bioload would appear to be far heavier than the cumulative effect of 11 fish...

@fcmf after having a tank for breeding snails, now having a tank for the baby BNs, and adult BNs in 2 tanks, I can say that all are all quite high up there on the poop producing scale. 
Constant grazing = constant pooping   

I'm sorry to hear that 

If there were two of them sparring, it could well be that one came out on top at the expense of the other.

I read something yesterday that is worth using to help explain certain problems in stocking tanks.

The questioner asked about keeping a pair of dwarf gouramis in a 40 litre tank. Several people said no, it's too small, but someone else said it would be fine provided there were lots of plants so they can't see each other. Then the real fish expert replied. I can't quote him directly (copyright) but the gist of his comment was that fish make two sorts of chemical, pheromones which are understood by fish in the same species, and allomones which are picked up by all the other fish in the tank. Aggressive fish like dwarf gouramis send out lots of aggressor signals, the filter can't remove them so the other fish live in constant fear. Then he used a comparison that would mean something to everyone.
If you shut a cat in a room which has a vicious dog chained in one corner, the cat will pick up the signals from the dog and although the dog couldn't reach the cat, the cat would be terrified.


I'm going to use that to explain things in future 

Once upon a time, many years ago, I worked in a hospital pathology lab, the chemical pathology lab to be precise. You would be amazed at the number of things we tested urine for. And that was just chemical pathology, there were other pathology labs as well.
If we excrete these chemicals, fish excrete similar things. And all the things we didn't test for in the lab. We may grow bacteria to 'eat' the ammonia made by the fish but they don't 'eat' anything else. So these other things build up in the water between water changes.
So yes, it is these other things excreted and secreted by the fish that is the reason we do water changes. Nitrate is just an indicator that everything is building up but if we have lots of plants so that nitrate doesn't build up, we still need to do those water changes.

This probably needs someone far more knowledgeable as chemistry than me to answer but as I understand it, activated carbon adsorbs organic compounds, so that logic would stand.  What is your water change regime like on the tank?  Using your example, it would also stand that after a big water change the fish should feel better as the chemicals in the water would be reduced.

And there is the other reason for water changes - plants need minerals, and the tank needs carbonate to keep the pH stable. These get used up and need to be replenished. Water changes are the simplest way of ding this.

This is something I've never quite understood. If the carbonate/KH in tapwater is 2, yet the KH in a tank is 3 due to having Tufa/limestone rock in it, then surely each weekly water change slightly dilutes/reduces the KH? Is it that, if the weekly water change didn't take place, the tank water would naturally reduce from 3 to 2 and potentially even down to 1 as the carbonate would get used up?

@Matt The tank is currently producing 25ppm of Nitrate per week, it was just over 34ppm/week but adding plants has I think caused the reduction. I deliberately reduce Nitrates back to 20ppm each change with on average a 40-45% change twice weekly. I have virtually no dKh (0.5) and dGh is 2.5 so I am diligent on changes, tank pH is stable at 6.2. Since adding hydroponic terrestrial plants to this tank as well I have started adding a 1/4 dose of nitrate free liquid fertiliser.
The thoughts on the carbon were largely clutching at straws as I can't see an obvious reason for the Severum not eating, everybody else is literally hovering food down and he just sits in the middle of the pack watching food pass him by. I'm am feeding 4 times a day because of the number of rapidly growing babies.
The fish is otherwise looking fine, active, good colour, free swimming and if it weren't for the fact that I'm watching him during feeding time I would have said he completely settled. Maybe he is snacking between meals (kidding the others finish every scrap within 60 seconds)
I'm not actually panicking just yet, given his otherwise good condition I will give him more time in case it's a settling in thing.

Thanks @Sue I will try that, everybody else will love that I'm sure. Let's hope they don't cotton on and all start wanting special treatment I will also ask what the shop feeds as well.