I see GH and KH also dropped when you did a water change. There is some source of minerals in the tank.
Yes it would. I am using pure R/O water without any tap mixed in. The flouramax seems to have a high mineral content.
I would put a small amount of everything that is in the tank or filter into a separate glass of water and test each thing separately.
Glass A = Pure tap water, just add dechlor
Glass B = A handful of the material you are using as substrate...
The verdict was the Miracle grow organic mix will throw the phosphates off the scale. I didn't bother with the cap since I want extra minerals using R/O. When that runs out I will do a tap & R/O mix to keep my GH/KH within range.
Start with just tap water and dechlor, but add however much fertilizers to each (one fertilizer per glass) that you are adding to the tank. Maybe one or more of the fertilizers is actually a blend and is adding more than you think.
I am adding no fertilizers with one exception. When I first setup the tank I dosed enough KNO3 to get nitrates to 5ppm. I also added a small dose of plantex GSM + B and chelated iron. That's all the fertilizer this tank has had.
You can continue with the fishless cycle while you work it out. Water changes are not a problem, as long as you re-dose the ammonia to keep the bacteria growing.
Water changes can be good. These bacteria do not grow so well when the ammonia or nitrite are too high. Do enough water changes to keep these under 5 ppm.
This I did not know! Thank you. I thought besides temperature the limiting factor was the ammonia/nitrate. I will continue water changes to keep things more normal.
A strong 'plant-swamp' smell might be from a strong odor algae or other organism. Blue Green Algae, aka Cyanobacteria is often diagnosed by this smell.
This is the odor it had. It was not overwhelming however. The hydrogen sulfide and ammonia smell I am familiar with. Those were not present.
Thanks for all your input!