Now you got me thinking about water changes; in many ways, I think it is like any other tool in the hobby.
For example, if your anubias is covered in algae due to unhealthy conditions, then you fix those conditions. What do you do?
1) Treat the old leaves and hope you don't treat them to harshly and destroy the tissues, plunk 'em back in.
2) cut all of the old leaves?
3) cut the leaves off one at a time as new ones pop out?
All the way hoping the rhizome isn't ridden with spores and the plant can recover?
So the use of the water change should be relative to the situation. In other words, generalized notions of change lots of water or change little to no water are well simply that - generalizations.
I would say that some strong advocates of heavy water changes may stop to think when I suggest one 100% change before lights on and one 100% at lights off. Or maybe that would be ok? Never tried it - and I won't unless I hire someone to do it for me 😀.
However, you can't change none! Even nature changes water!
Josh
I suggested water changes to reduce the overall level of nutrient in the tank. I am telling you this because I faced exact same problem with Rotala. I had very hardwater, with 20+ ppm nitrate present. I cut it down with RO and dosed way less. Things improved dramatically over a couple of weeks.
I am in this hobby for a long time now and have seen all sorts of arguments against hardwater/software , EI/low dosing, Trace toxicity/K overdose etc etc.
The problem is that there is no proper controlled experiment demonstrating the effect of individual parameters while keeping every other variable fixed. People just say things based on their own settings.
I can not tell you the upper or lower limit of any nutrient, because it;s a relative thing. There are tanks where some have grown excellent Rotala and Ludwigia with EI level of nutrients and there are many examples where lower levels seems to do better. You can not compare these two because you don;t know exact parameters of the tap water, type/how old is the substrate, light intensity, water change frequency, aeration, fish load etc. etc.
But in my personal experience, hobbyists run into more problems when dosing excessively or using hard water.
Your water parameters are great. 5-7 ppm of potassium, less than 5 ppm of nitrate, 0.5 ppm of phosphate, 1 ppm magnesium and about 0.1 ppm of trace should be enough, provided you are not going crazy with lighting, dosing enough CO2 and feeding your fishes. If you see deficiency of iron, you could add a bit more via any branded iron fert or by buying in chelated form.
Again, what I am saying is mostly likely to fix any issue you are having but it's not guaranteed. I just don't know what are the parameters of your tap water. You might have crazy high nitrate like mine, or you could have high zinc or whatever. If you see things are not improving, you could try to use RO (as I did) to improve things.
For example, here are few pictures my Rotala transitioning to better form upon introducing RO and dosing only with Tropica specialized + occasioal potassium in the form of potassium carbonate (which also maintains the KH)
1. First 10-15 days in tap water(very hard), Rotala barely grew, with top leaves bending down which I find to be a classical sign of things are not going well. (CO2 is supplied enough)
This picture is after cutting down with RO and dosing less. Plants resumed decent growth within days.
Now the pearling is also great.
It was just one example. I have had such experiences before as well. I don't know if it's excessive calcium/magnesium blocking iron uptake/ high pH precipitating iron/ excess nitrate ding something crazy or something else.
