The "half year later" report:
The tank is working fine now. I have some aestetically issues I can live with, and some nasty consequences of bad initial choices. Let's summarize my tank:
1- 120x50x50 cm (300l)
2- Eheim ecco-pro 300
3- 3x54w T5 (HO I think) raised 30cm without reflectors nor hood (I use the "spare" light to keep the room lighted
4- no CO2, no ferts, no dosing, no nothing
5- 10-20% water changed every spare week
Critters:
- ~20 red cherry shrimp (they were around 80 but...)
- 2 botia striata (they learned how to hunt my red cherry shrimp)
- 3 botia yoyo
- 6-8 Siamese Alga Eater
- 7 otocinclus affinis
- ~25 danio rerio
- 2 gourami trichosomething (both females, I think)
Growing plants:
- a lot of egeria (I keep it because it grows fast, and I'm preventing a new cyanobacteria's attack incoming from the substrate)
- few eleocharis parvula (just planted)
- Microsorum pteropus 'Windeløv' from the day 1... I had few hopes about it, and it keeps its bushy looks... I think it's the plant I had more success with (except the fast growing ones I had to keep out)
- hygrophila corymbosa siamensis
- rotala rotundifolia
- echinodorus (I'm not sure the variant now)
- criptocoryne (I'm not sure the variant now)
Dieing plants
:
- alternathera
- pogostemon
One thing that surprised me:
- my SAE decided to develop an addiction to alternathera and pogostemon... from time to time they EAT those plants' leaves... the pogostemon now have a really sad look
As I said, the tank is running fine, but I think it will be a disaster soon. Why? Because I took a bad choice from the base.
The substrate I choosed was not a bad idea: using garden substrate it's a good thing that helps plants to root and be fed. BUT I did NOT checked its chemicals properties, and my water has been suffering from it.
Additionally, using stones to "raise" the level of the substrate has proved to be a bad move too, because it left a lot of "holes" on it. Those holes became a time bomb. They been filled with water, and that water became a nice nich for cyanobacteria to grow. The "holes" near the glass are full now, and I bet a lot of holes I cannot see are keeping a nice colony of those nasty bacteria too.
It means sooner or later I will have a cyan carpet flowing from the ground, and it will be too hard to fight.
Solution: learn from there and start from scratch. More or less.
Soon I will make a call to arms to a bunch of friends and we will empty the tank, keeping the plants and critters, the filter and it's bacteria colonies, and some other things while we get rid off the garden soil.
My idea is to put a thin carpet of aquarium nutritive substrate (1cm or so), a thick carpet of silex sand (used in pools' filters, it's chemically neutral, it's supposed) and some of the big rocks and black gravel to scape.
The initial though is to clear all those things with water from the tank WC, trying to give a chance for some nice bacteria to stablish.
Re-plant, refill and put the critters. With the cicled filter and using the most possible water from the stablished tank, I think the tank will be near cicled. I will test it daily again to be able to put the critters out of the tank if I see nasti peaks of bad chemicals, but I think I will NOT have them now.
Any additional thoughs? The plants will be used to my water, and I think I will not need additional "soil" this time. But the idea is to move a bit more in the direction of a low-light low-tech, with spared water changes as I do now.
I will keep you informed in another "journal", if I can put my ideas in the real world...