# Ferts & TDS



## jameson_uk (11 Jun 2018)

I know some people use TDS to work out when they might need to add (more) ferts and this got me thinking.

I added my weekly dose of TPN+  I did a quick before and after TDS reading and it didn't go up.  I was expecting an increase to be relatively instant but is there some sort of lag to be expected after adding the ferts? 

Out of tap my water is consistently ~320 so given I do weekly 50% water changes would the tank reading 320 suggest that things are back to tap levels?

The plants are always my main clue as to what is going on but being colourblind sometimes makes it difficult to see when leaves are changing colour.   Is  there  any  merit  in using TDS as a proxy for fert amounts?


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## tam (12 Jun 2018)

You need to wait long enough for the ferts to mix evenly with the water - how fast will vary - I usually test anywhere between an hour and the next morning (basically when I remember).

TNC+ dosed according to the bottle (7ml in a 70L tank) raises my TDS by approx. 18/17, TNC Lite by 4/5. 

I don't think you can use it to determine when you need a dose though as other things raise it, so it might drop 5 as the plants use up the ferts, but go up 5 from the fish food, hardscape leaching, plants/leaf litter decaying etc. It appears superficially the same but your ferts are gone.

I don't know how higher tech tanks work, but generally mine gradually rise in TDS (not drop) even when plants appear short on nutrients - either they are exhausting one type and not using the rest or the fert part of the TDS is being replaced by TDS from other sources (likely a bit of both).

Is your tank at 320? Usually tanks run at least a little bit above tap level from the extra going in.

As you are changing 50% a week, you can basically add lots of ferts, as you'll keep it steady overall.


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## Edvet (12 Jun 2018)

In greenhouse agriculture feeding is often automated and steered through a TDS meter. Don't know the exact numbers and or timing but they measure the effluent and if it gets to low they add ferts from a reservoir.
There are even smaller systems for the home indoor herb grower


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## ceg4048 (22 Jun 2018)

jameson_uk said:


> The plants are always my main clue as to what is going on but being colourblind sometimes makes it difficult to see when leaves are changing colour. Is there any merit in using TDS as a proxy for fert amounts?


This is really an unnecessary complication. Just dose regularly and carry on. You'll never be able to tell when plants need a dosing just from the TDS.
If you are waiting for a color change then by the time the change has occurred then it is already too late and the plant is suffering a nutrient deficiency.
When the nutrient level is high the uptake rate is high and the nutrient storage level is high. When the nutrient level is low the uptake rate will slow and the plant may dig into the nutrient reserves.

Additionally, TDS levels will rise as the pollution level in the tank rises, so with all these factors, you will not have a reliable indicator.

Cheers,


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## J@mes (22 Jun 2018)

Edvet said:


> In greenhouse agriculture feeding is often automated and steered through a TDS meter. Don't know the exact numbers and or timing but they measure the effluent and if it gets to low they add ferts from a reservoir.
> There are even smaller systems for the home indoor herb grower



Ooh I love fresh basil


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## AverageWhiteBloke (23 Jun 2018)

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.


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## AverageWhiteBloke (23 Jun 2018)

Edvet said:


> There are even smaller systems for the home indoor herb grower



You seem to be well informed ED


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## AverageWhiteBloke (23 Jun 2018)

I guess to summarise, just wondering if you can use a TDS pen to get an idea of ferts in a low tech tank where plant growth is sub optimal but maybe in the case of higher energy and co2 it would give a false positive reading if you like as the amount of ferts consumed is masked by the waste produced with heavier plant growth and the bi-products associated with it?


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## tam (23 Jun 2018)

AverageWhiteBloke said:


> I guess to summarise, just wondering if you can use a TDS pen to get an idea of ferts in a low tech tank where plant growth is sub optimal but maybe in the case of higher energy and co2 it would give a false positive reading if you like as the amount of ferts consumed is masked by the waste produced with heavier plant growth and the bi-products associated with it?



I think even low tech you can get a false positive from fish waste or even decomposing plants and substrate and hardscape that may be leaching small amounts too.


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## Parablennius (23 Jun 2018)

Hi
I use my TDS pen to judge daily increases due to ferts etc so that on 50% water change day,  soft tap water made up to GH5, KH2, takes me back to the same start point on Sunday.
cheers


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## AverageWhiteBloke (23 Jun 2018)

tam said:


> I think even low tech you can get a false positive from fish waste or even decomposing plants and substrate and hardscape that may be leaching small amounts too.



For sure there's quite a lot of things to take into account that could affect the reading, in the big scheme of things admittedly the jump isn't that much but it is apparent. If you look at the trend you can see there are few anomalies other than about week 15 which was after a prolonged spell of dry weather then it rained heavily for a few days which upped the KH of my tapwater a little.  Other than that everything seems to be fairly consistent up to this week when there was a noticeable increase in plant growth. The result wasn't what I was expecting considering the plants probably consumed more of everything this week. Obviously I will have to carry on for a few more weeks just to see how consistent that is or it levels out again but in the case of using a TDS pen to measure fert concentration those results might be interpreted as plenty left when law of probability says there was probably less than the previous weeks..question is if it wasn't fert, what made up the difference? Removing the floating plants are something that's threw it out of wack though.


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## AverageWhiteBloke (23 Jun 2018)

Just been looking at the figures the graph was built up off which makes things a bit clearer, based on the last 8 weeks stable tests on average, pretty much consistently  tank TDS rose by 21ppm over the course of a week. On the week of growth and filter change the tank rose by 36ppm, I wonder if co2 starved plants were maybe gaining carbon from carbonate which they no longer needed to do with plentiful co2 combined with excess plant waste?

Just realised there's too many maybes to find a definitive answer


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## ceg4048 (25 Jun 2018)

Hi AWB,
              As I mentioned, the graph cannot isolate how much decline is due to nutrient uptake and how much rise is due to substances introduced into the water column. Nutrients are also pulled from the substrate as well as the water column and the substrate itself binds some nutrients. So the nutrients are dispersed and this therefore tells you nothing. For example, when you dose micronutrients, these are all metals, such as iron. The plant will uptake these for about and hour after dosing and then they will curtail the uptake. The metals will then bind to other substances in the water column and fall to the substrate, where they can be taken up by the roots. Waste products such as urine and feces, as well as uneaten food will decay and produce Ammonia, which the plants will also uptake, sometime preferentially compared to NO3. This is one of the reasons that a planted tank is generally more healthy for fauna.

Unless we can specifically isolate which nutrient as well as which uptake rate the system is applying to that nutrient, we really do not know the removal rate of nutrients versus the ejection rate into the water column of  other susbtances. This is regardless of high tech vs low tech.

Those who use this method are effectively dosing regularly because the trend is regular and therefore they are simply maintaining the nutrient levels in the same way as those who just dose regularly.

Cheers,


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## AverageWhiteBloke (25 Jun 2018)

Cheers Clive, I was also rapidly coming to that conclusion. Was having one of them days Sunday when I had the thousand yard stare at the tank contemplating the what ifs, realised there was too many what ifs too contemplate  Couldn't really come up with anything definitive so it's back to good old fashioned plant health monitoring. TDS meter did have some uses when I probably OD'd the Osmocote in the original setup. I wasn't dosing anything at all for a long while other than traces. The graph I put up there goes back a lot further than that and there was a constant decline in TDS over a period of time signifying when it was wearing off. I jumped in with Macros when I hit the 150ish TDS which I was hoping to sustain that hardness  for the GBR's and the first signs of deficiency. Dosed the same very week since and it seems to be about right although I may up this a touch going forward to match up the co2 induced better growth.

I know this goes against the EI mantra of pile it in and fire and forget but I have to say this is the second time I've set up a tank in this fashion rather than yellow DC's and EI from the off and its been good to me problems wise. Obviously I've used the lighting as the limiting factor but I would suggest more people try this approach of seeing how little lighting they can get away with and gradually ramp it up over months rather than weeks. Going up co2 and ferts, give it two weeks or more and another notch up on the light seems to pay dividends.


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## AverageWhiteBloke (25 Jun 2018)

Got that the wrong way round. I ran without co2 for probably about six months, started adding some fert then introduced co2. Seem to get the plants established without encouraging algae then once you hit the Algae encouraging phase the plants have already won the war. seems like if you start out eutrophic and high co2 it's a 50/50 ball who's going to win.


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