Hallo from Germany

[ALara]

Hello my name is Larayel, Lara for short. I am American born and raised in USA (Southern California then South Missouri) I moved to Germany 13 years ago.
I have begun an aquarium hobby again after many years. I have been having problems with white moldy looking growth in my substrate for a couple of months now and am very much unfamiliar with this. I cannot find online what it is or why it is happening and I am keen to learn to be a better fish mom. Please forgive me for the picture, I am pretty desperate to learn what is happening so I have not cleaned it yet. I have a 40L glass aquarium with an Eheim 80l inside filter. The temperature is roughly 25° celsius, the water is naturally hard here so I have been usually using a softener, but not the last month because the fish person at the store said tetras are good in alkaline water. I do partial water changes (20%) every two weeks and each introduction of new water is treated with Detoxol to remove chlorine, nitrates, ammonia etc. I do not over feed but it seems the type of food I use sinks too fast and I think a lot of this is eaten by the hunter snails and corydoras and golden shrimp but I feel like I am failing the hobby because almost immediately this white stuff appears again, and algae blooms. I am desperate so I have come here to learn and be better at my tank. Also will mention none of my plants stay alive either. I buy plants and within weeks they are dead. I am unsure if this is because the light might be insufficiently providing the source they need to grow

 

[emeraldking]

Firstly, welcome to TFF...
Such white layers can have different causes. One of them isd overfeeding. But by reading your text, it's not that much. But even if it's not that much, if that food is not eaten by fish, this can be a result. Not all fish will go hunting for food once it's on the bottom.
But also an instability in your water parameters could cause this.

Fish like tetras, come originally from soft water areas. But I do have to say that depending on the type of tetras, that hard water won't be a problem. I myself live in an area with harder water. I have number of tetra strains that thriving very well in my tanks. But mine are tank bred specimens. If they would come from the wild, I would definitely use softeners.

Btw, wir sind Nachbarn. Ich wohne in die Niederlande. Sehr nah zu die Deutsche Grenze.

 

[ALara]

Hallo Nachbar! I am in the Hessen region of Germany. Very sweet little area out of the city in the "Dorf"
Should I keep doing water changes more often or should I change foods? When I do the partial water change I am always sure to vacuum up that area but it stubbornly comes right back so quickly.

 

[emeraldking]

Well, a couple of extra water changes won't harm. Certain types of food can stick to gravel. When that happens not all fish are willing to eat from that spot. Which does create such white (and could even be green) layers on the gravel or sand. There are fish foods that contain too much bonding substance. This is meant to not clowder the water. But it can stick to gravel.

I'm close to Nordrhein-Westfalen (close to Gronau).