I have a 180 gal community tank with live plants, nothing difficult to grow(java ferns, anubius, water sprite) The tank gets 10 hours a day of light plus natural light. I was adding Seachem Excel and Iron to the tank once a week , when I did water changes. Everything was fine, PH was good all other levels good. I increased the dosage of Excel and Iron and now I find my PH is stady around 6.2-6.4 and my nitrates are up. My plants look bad and new growth doesn't stay green for long. My question is....does Excel lover my PH like CO2 would? Would the lower ph harm my bio filters to make the increase in my nitrates? If the answer to the first two is no, how do I safely adjust the PH towards neutral?
There is no reason to worry about the pH. You are well within the range that fish and plants are fine with. How much light do you have, in wattage and bulb type, reflectors? You may have low enough light not to need to dose anything except what is needed to maintain the GH of the tank. Excel and iron will not directly affect the pH or the amount of nitrates in the water.
What you saw with the plants was a secondary effect, indirect.
By adding more, you now increased uptake of something else, likely PO4, and it ran down to zero.
Your Carbon and NO3 obviously did not limit growth, so it was something else.
Since you only added a couple of things(Fish food, Excel and Fe), it's likely you got barely enough PO4 or K+ etc from the fish waste alone to support a stable system and growth rate.
Adding more Carbon drove what little you had, to an extreme.
Then you get poor plant health/growth.
What you can do is a modified EI routine, basically do once a week water changes, say 30-50% and dose EI, but only at most, 1/3 the suggested amounts.
1/4 ought to be fine.
Excel is going to cost a bit on a 180 gallon tank, best to leave the light etc the same and add CO2 gas.
I have 4 36" bulbs all 30 Watts 2 - flora sun 2 - flora-glo Yes to reflectors.
With that amount of light you won't need to dose a lot of anything. Have you read about Diana Walstad's el natural method for low light tanks? Or, read here about Tom's non-CO2 methods.