tiny black spots on leaves

[eddtango]

I can see tiny black spots on the leaves of some of my plants esp. the leaves on the bottom of my stem plants and crypts. Are these algae? Or dying or old leaves because they can't get enough light? I suspect it to be some sort of nutrient deficiency,but I add Flourish 2x a week and Leafzone Iron and Potassium 2x a week ,I do a 20% water change every week. There's a Hagen CO2 setup for this 32 gal tank,bubbles are at 1/10 sec. and plants are growing like crazy(esp the H.polysperma and H.siamensis). Is it normal for these stem plants to have the bottom leaves in this condition? BTW,the pH is about 7.2.

[Sleepy_lancs]

I am not very firm about this but I suspect the black spots are BBA forming. Since there is no mention of KH value in your help outcry, I would suggest lowering your PH to below 6.8 using CO2. The reason for doing so is to prevent CO2 from forming CO3. Plants needs more energy to get their carbon if its in CO3 form. Algae which needs very litte carbon will always increase the PH value to deprive plants from getting their carbon.

[liuhao]

very easy. see if you can scrap the black spot off. if yes confirm algae (most likely BBA).

[planter]

I use to have this problem too, mostly on my slow growing plants. I increase my Co2 input and the black spot is gone in no time.

[loneranger]

gd method but nvr try b4