I've been lurking around here for a while, and I think it's safe to say American and Asian ideas on keeping fish differ strongly from European. But I guess it's just another view on things. If you believe the fish are really happy, then so be it, I'm sure you're right.
Please don't think of this post as a personal attack. I'm just trying to outline the different approaches to keeping fish. "Barebottom".... I'm sure it's easier this way, but is it better for the fish? I don't think so.
Discus need clean water, we all agree on that. However, there are better ways to keep the water clean than to go "bottomless". Some examples:
- Add real plants in stead of plastic ones: plants will reduce nitrates, phosphates and what not and introduce oxygen. You can't do this anymore, since they can't root anywhere.
- Get a large enough tank for your discus. IMHO (and in the opinion of every person I know) your tank is too small for 8 discus. In Belgium/Holland we count at least 50L water per discus, so for 8 discus you'd need a 400 liter tank (+100 gallons). Tankmates will count extra towards the water amount. So for your fish, a 500 liter tank would be required by Belgian/Dutch standards (about 130 gallons I think that is).
- Add a "sump" (I think that's the English word for it, an extra tank pure for filtration of at least 100L). So total amount of water is increased by another 20%.
- ....
That's how Discus are kept by the people I know in real life, and they only have to do monthly water changes. Just like everyone who has an aquarium. Their discus are completely healthy and spawn on a regular basis.
Oh, and corydoras like to burrow their nuzzles in the sand... it's kinda sad they can't do that anymore. My corydoras sometimes stick their entire heads in the sand looking for food and it's really fun to watch to see all 9 of them doing that next to each other. Always brings a smile to my face.
Once again, this is just my personal opinion and opinions differ. But we're all entitled to express them, are we not?
In any case, good luck with the tank and the fish.