Interesting one, I use a TDS meter more for the fish than the plants although I can glean some ball park fert information from the results combined with plant health monitoring. I dose the same amount of ferts per week and test TDS just before and just after water change weekly. My water is very soft out of the tap (round about 80ish). Because of the inhabitants of German Blue Rams mainly which I'm hoping to spawn at some point although rapidly coming to the conclusion I've missed the boat on these two, looks like they have a phase of spawning when very young which tails off as they get older.
Anyway, back to the TDS, been running the tank semi low tech, sponge air driven filter for breeding purposes as well as not to suck up my young RCS although I had a spare co2 setup kicking around so had this bubbling away at 1bps, wasn't big on co2 as obviously the air filter was causing a fair amount of surface disturbance and there wasn't a lot of flow in the tank, hardly moving if at all in some areas I would say. The DC was running at a dark green, was going to use LC at first but I'm not about to dose daily and couldn't be bothered trying to set up an auto doser, trying to keep thing simple. My lower level substrate plants were failing a bit Helfereri, S. Repens and MC was surviving but not exactly thriving. All in all plant health was fine, no sign of deficiency on other plants, floaters and easy stems looking healthy enough albeit growing very slowly as if in a state of suspended animation
Algae wasn't an issue but the fish were, got some Ottos and shrimp in there and the first sign of weakness from the lower level leaves they would trough the leaf and leave just the stem!
Decided I was going to swap out the air driven sponge and use a small canister filter I had kicking about and use the sponge off the air driven as a prefilter to get the media in the external seeded quicker and prevent anything getting sucked in the canister. The main difference I have here is the DC is now a nice lime green colour at lights on and some better flow around the tank, no changes to ferts which I'm dosing from same bottle using a syringe in such a small tank and no change to the bubble rate, same weekly ritual as before. So, looking at my TDS graph which I use to monitor when its getting a bit high you can see that over a period of time there's a trend to lower TDS, starts off high as I used Osmocote in the substrate on setup which I'm guessing is slowly wearing off if not totally gone by now however I seemed to hit a bit of a sweet spot where week after week the TDS was averaging out and plant health was good other than what appeared to be some co2 related issues.
The noticeable difference was that plant growth boomed, stems filled out and shot to the surface, all other plants including the MC showing new growth and just generally better. I'm guessing that this tank was right on the edge of coping with my light setup and crying out for that additional co2 and flow. My assumption would be that the plants would have waxed my ferts with the new growth and I would probably have to look at dosing a bit more to take up the slack, the exact opposite going off TDS happened.
There was a jump up. I don't really feed much in there as the ottos get a slice of cucumber twice a week which the shrimp also partake in so other than add a couple of crumbs of tetra prima for the others I can't really blame on over feeding as the difference. The only other things that spring to mind for me could be either the external canister is producing "something" although I would assume it would just convert from one to the other not add? AFAIK gas doesn't show up on a a TDS reading? The other suspect might be waste bi products from plant growth? maybe increase the water change. Or the long shot might be that I removed a couple of cups of duck weed to get some better light penetration down to those substrate based plants, maybe I seriously under estimated floaters and the amount of fert they can suck out the column but you would have thought the new growth from other plants would cancel each other out.
What would your thoughts be on that
@ceg4048 ? I know this is all a bit unnecessary and anal but I just like to experiment to get better understanding.