High nitrates do not kill fish- but, they do have the capacity to stress fish over time. This stress, then, can lower immunity and allow pathogens ( bacterial infections such as aeromonas, for example) to get the upper-hand. Some fish are more prone to high nitrates than others.We've had a 30 gallon planted tank about 3 years and it has been very stable for quite a while (nice plant growth, healthy fish), thanks in part to great advice I've gotten in these forums in the past! It's low-tech, not CO2-injected.
Here are the current parameters:
Nitrate 80+ (seems high to me, but it's been fairly stable at that level for the last 10 months and the fish seemed fine)
GH 8 or 9 (8.5?)
Recently things seem to be out of balance:
- Growth of algae type 1. It's kind is green and forms long strings, looks like a green cloud where it attaches to plants and wood. I remove as much of it as I can with my water changes (every 1-2 weeks).
- Growth of algae type 2, which from my googling I think is black beard algae.
- Some of our younger endlers look too thin (top to bottom), like they're missing the correct curve of the abdomens.
- Some of our endlers sometimes rest on the bottom substrate for long periods of time. Usually when I notice this I do a water change right away and the behavior stops, but most recently they started to do rest there about 4 days after a water change, which is awfully short.
- Our betta died, the first fish death in over a year. The betta was large when we got him and we've had him about 2.5 years, so he was probably an older fish (I read they live 3-5 years), but it's still a concern.
I just changed our timer so the light will be one fewer hour a day.
In Googling the black beard algae I saw a site that recommended dosing with Seachem Flourish Extra. Do you agree?
What other steps would you recommend I take?
I would never think of 80 ppm in nitrates as an indicator of a healthy system.
However, I have learned on this forum that, in some situations, a high tech aquarium with high density plantings and fast growing stems-- 80 ppm is not high. That there is a difference between nitrates from dissolved organics and fertilizers.
It doesn't appear that you tank falls into that category, however.
How often do you do water changes? What volume?
How many fish are there in tank? What types?
How often do you clean gravel substrate?
How often to you clean up plant debris?
How often do you maintenance filter?