I was experimenting with my tank the past two weeks due to algae and nutrient issues (first noticed yellowing of old growth, brown spots on one leaf, new leaves fine). The deficiency issue started out a yellowing, but this plant is different, dark veins and darker in general and the same appears to be spreading to other s. repens. These two pictures were taken 2 weeks apart. I'm unsure what to do about it. my Ca in tap is 21.1 and Mg is 6.09. I've been dosing flourish comprehensive once a week as recommended and in the past week+ have been dosing iron and potassium and the plant has only gotten worse. I can only think i'm deficient in Magnesium or phosphate, which I ordered and now have but have not used. (I have not used it because after a large growth spurt from increasing liquid co2 and dosing flourish comp. iron and potassium the last two weeks I got GDA on the walls and don't want to give it more to munch on, but i do want to treat the deficiency at the same time). And I've heard a PO4 deficiency can cause GDA.
While other plants aren't showing it as severely as this one is here they are beginning to show the same dark veins and dark look, affecting old growth leaves only. Growth has been quick and the deficiency has picked up speed. I need to find out what this is and fast. The past few weeks i've consistently tested 10-20ppm NO3, but 0ppm P04 and I've been dosing the recommended amount of potassium to raise ppm to about 20, and dosing Iron as recommended, and flourish comprehensive as recommended and actually dosed it twice three days ago after water change hoping that the missing nutrient could be picked up by that extra dose. To no avail though the plant looks worse.
I gotta find out what this missing nutrient is or cut the lights and co2 to stunt growth and the moving around of watever mobile nutrient is missing. NPK or Mg I believe. 6.09ppm is in my tap, not sure if that's enough, I heard ideal is 10ppm but I guess it depends on growth speeds and plant mass? From the 6 or 7 times i've tested NO3 the last 2 weeks i've had 10-20ppm and the last 7 days have been dosing potassium (.25ml per day 2.5 gallon tank). So if I'm understanding things correctly this could be pointing me towards phosphate deficiency as that seems to be the only one i'm missing (never tested above 0ppm last two weeks).
I get a lot of confusing signs and symptoms and different pictures with deficiencies. Any help would be appreciated. I just started taking planted tanks seriously a month or so ago.
Bump: 8/06/19 (zoomed out) showing leaves in better health than images below
8/06/19 (zoomed in) the plant in question showing better health than images below
8/20/19 (zoomed out) showing leaves generally in worse health than images above
8/20/19 (zoomed in) showing plant in question showing leaves and veins dark, tips of leaves light
I have a nutrient dosing plan I created that I think is ok. And I have on hand: Flourish Nitrogen, phosphorus, Iron, Comprehensive, and Potassium. Along with API CO2 booster.
What I'm struggling with right now is two fold, solving the nutrient deficiency while resolving my GDA problem that has gotten worse day by day.
I did solve the GDA 3 weeks ago when I decided to do something about it. With 6hrs light (half), no dosing, no liquid co2, algae didn't return after cleaning it. Then after believing I had solved the issue, increased light to 7 hrs. .2ml of liquid CO2, .2ml flourish comp once a week, .1ml (.07ppm) Iron once a day, .25ml (1.59ppm) K once a day. GDA was ok first few days, guess it had to build up to be visible but it's definitely back, even more so I'd say. Before I did something about it I wasn't dosing anything not even CO2.
I just don't know the more I think about it the more confused I get about how to approach it. I already decided to reduce light back to 6 hrs. I don't think i'll reduce co2 since a lot of people usually talk about increasing it to combat algae. Which leaves dosing......I just don't know, if I don't dose my plants, at the rate the deficiency is going, could die in a week or two. I could dose minimally and give it a week and monitor plant health and algae and go from there perhaps.