# Total Dissolved Solids changes over time in tanks with no water changes



## sciencefiction (24 Apr 2014)

Ok, so I am a bit puzzled between the Total dissolved solids reading of two different tanks which haven't got water changes for a good while and I thought you guys may know.

Tap water(original readings in both tanks)
TDS: 300-ish
Gh: 12
Kh: 8
Ph: 7.4


Tank 1:
Soil type 1
Heavily planted. Non-fertilized ever.
Fully closed with lid, little to no evaporation
No water changes for nearly a year.
TDS reading: 200ppm
Gh:7
Kh:2
Ph:7.4

Tank 2:
Soil type 2
Heavily planted. Non-fertilized ever.
Open , water evaporates fast enough.
No water changes for 7-8 months
TDS reading: 500ppm
Gh: 14
Kh: 4
Ph; 7.4

What do you guys think, why did those two tanks went completely different way as to water chemistry?
Is it because the soil is different maybe?
Or because the enclosed tank with low TDS has got no evaporation and little top ups?
I have other enclosed tanks that get no evaporation and the TDS still rises over time if I skip water changes so that's why I am not certain why the TDS in one of the tanks dropped significantly and the water is now soft in there, though the red cherry shrimp are still doing well in it, overrunning the tank.
And also why did the Ph remain the same?


----------



## NC10 (24 Apr 2014)

I'm no scientist, but know a bit about distillation, which this all boils down to I think. (excuse the pun lol)

The tank with no lid which you keep topping up with 300ish TDS is only going to evaporate pure water, so leaving anything else that originally went in with the water behind. You keep topping up with that water and obviously over time the TDS will slowly creep up.


----------



## sciencefiction (24 Apr 2014)

Thanks NC. I think this could be one of the reasons, only that this doesn't happen in my other enclosed tanks with lid on which is why I am not sure. Maybe I haven't left the others without water changes for long enough but the TDS the least steadily rises in them too as I've left them for 2-3 months sometimes. They've got no soil, just plain sand.[DOUBLEPOST=1398373899][/DOUBLEPOST]Just to note if it matters that both tanks are fed daily too with similar food if that makes a difference despite the one with decreasing TDS having just cherry shrimp inside.


----------



## NC10 (24 Apr 2014)

If you're not doing water changes then surely the TDS will creep up anyway over time, through plant matter, fish waste, food etc? Just that it will be faster without a lid and adding 300 TDS water.

If you're not changing the water or feeding at the same time, have slightly different planting or lighting, I don't think you can ever really compare the tanks. Way too many variables.


----------



## sciencefiction (24 Apr 2014)

The reason I am asking is because I want to try and reproduce the "soft water" tank but what normally happens when I leave a tank with no water changes is fast rising TDS and Gh no matter what.

Light is obviously different in these two tanks but the low TDS tank got its plants from the high TDS tank so some plants are the same.

They both get fed daily with NLS pellets mostly.


----------



## NC10 (24 Apr 2014)

That's what I mean though with too many variables. How many plants or fish in each tank? Are they exactly the same type and amount? Are the bulbs exactly the same brand/age and changed at the same time to ensure equal intensity? Same amount of water change at the same time?

It's obviously the same water going in so all you can do is replicate the tank you like as close as possible. Taking a lid off/on, same plants, same amount of plants, same lights etc

That's all you can do really, but even then they're not going to be exactly the same, near as you'll get it though.


----------



## Andy D (24 Apr 2014)

NC10 said:


> I'm no scientist, but know a bit about distillation, which this all boils down to I think. (excuse the pun lol)
> 
> The tank with no lid which you keep topping up with 300ish TDS is only going to evaporate pure water, so leaving anything else that originally went in with the water behind. You keep topping up with that water and obviously over time the TDS will slowly creep up.



I would agree. 

To put some figures too it let's start with 10litres of water. TDS is 300ppm. If 50% of the water evaporates (and it would be pretty much pure water that evaporates leaving everything else behind) you are left with 50% of the water with 100% of the original TDS now giving a TDS of 600ppm.

When you top this tank back up you are adding water with a TDS of 300ppm therefore you end up with a TDS of 450ppm ( (600+300)/2 ) 

If you wish to keep the TDS at 300ppm you should top up with water with zero TDS (like RO). This is exactly what salties have to do. When setting up or doing a water change they use RO and add salt. When topping up due to evaporation they use straight RO.


----------



## sciencefiction (24 Apr 2014)

I have 5 tanks altogether. The ones that get water changes have their TDS, Gh, Kh, Ph non variable, specifically the last 3 and I've had them for years.  The TDS increases by the end of the week. I do a water change to bring it down. Hence I assumed TDS always increases no matter what. They all have different light, fish, plants, etc..

I know when one doesn't do water changes theoretically the Gh increases over time because of the build up from the top ups but the Kh decreases which is what happens exactly in one of the tanks. But the other is just doing the opposite and turning into a soft water tank.[DOUBLEPOST=1398377309][/DOUBLEPOST]





Andy D said:


> If you wish to keep the TDS at 300ppm you should top up with water with zero TDS (like RO). This is exactly what salties have to do. When setting up or doing a water change they use RO and add salt. When topping up due to evaporation they use straight RO.



I understand that guys. I find it perfectly normal for the TDS to increase over time.

My point is the 2nd tank has decreased it's TDS and Gh overtime turning from a hard water to a soft water tank on the contrary to the other tank in which the water has turned harder and harder.


----------



## NC10 (25 Apr 2014)

I'm probably missing the point you're trying to make, but of the two tanks you're talking about, 1 is uncovered and suffers from evaporation and the other is covered and doesn't suffer from evaporation. 

They both haven't had a water change for near enough a year apart from the one without a lid constantly needing top ups. (adding TDS which you know) 

The only thing I can take from the decreasing TDS tank, is that the plants are using enough nutrients to slowly lower it, whereas they can't keep up with the amount being topped up for losses through evaporation.


----------



## sciencefiction (25 Apr 2014)

NC10 said:


> I'm probably missing the point you're trying to make, but of the two tanks you're talking about, 1 is uncovered and suffers from evaporation and the other is covered and doesn't suffer from evaporation.
> 
> They both haven't had a water change for near enough a year apart from the one without a lid constantly needing top ups. (adding TDS which you know)
> 
> The only thing I can take from the decreasing TDS tank, is that the plants are using enough nutrients to slowly lower it, whereas they can't keep up with the amount being topped up for losses through evaporation.



Well, yes, roughly said. The lid tank of course does suffer some sort of evaporation and gets top ups but not as often. I guess the plants have been using a hell of a lot of calcium and magnesium 
 The other one is open top with massive emersed plants too on top and heavily planted on the bottom so plenty of plants to use the nutritients. The emersed plants have flowered too so obviously rich in nutritients water.

The point I am trying to make is that I have 3 other planted LID tanks besides these two(sand bottom) with no evaporation and the TDS or Gh never goes down, the TDS goes up.  I don't do top ups on them. I do water changes to lower the TDS which creeps up over time so I don't think the close lid explains the difference in chemistry between the other two?


----------



## NC10 (25 Apr 2014)

The plants would easily use whatever calcium and magnesium there was in tap water over a year surely. 

It would be interesting to know what the TDS of the open top tank would be without the emersed flowering plants though.

Is it possible to put a picture up of your tanks and parameters or is it too much hassle? There has to be something very different for you to just pick 1 covered tank out and compare it with the open tank. Out of 4 covered tanks, why is one so different?


----------



## sciencefiction (25 Apr 2014)

> There has to be something very different for you to just pick 1 covered tank out and compare it with the open tank. Out of 4 covered tanks, why is one so different?



What do you mean?
The only reason I compared those two together is because they are both soil tanks and are the only two that don't get water changes.
Why would I compare them with sand bottom tanks that get 50% water changes weekly?

I have journals of both them tanks here on the forum

Tank 1(TDS 200)
http://www.ukaps.org/forum/threads/nano-walstad-tank-startup.28519/#post-346472

Tank 2(TDS 500)
http://www.ukaps.org/forum/threads/the-disaster.26889/page-3


----------



## NC10 (25 Apr 2014)

Those flowering plants look stunning.

I can't see anything other then that it's down to evaporation and the rate at which the plants can use minerals.

Magnesium and calcium hardens the water, so they're just not using them fast enough due to the constant top ups, keeping the GH higher. Whereas the one not needing so many top ups is depleted quicker, lowering the GH.


----------



## sciencefiction (25 Apr 2014)

The other 3 tanks, not current pictures but not much has changes to be honest.



 



 

I couldnt' find a full size picture of the third one but it's a juwel koral 60l tank with black hood on top[DOUBLEPOST=1398384883][/DOUBLEPOST]





> I can't see anything other then that it's down to evaporation and the rate at which the plants can use minerals.



Ok. Thanks NC10. I suppose there's nothing else to explain it. I am tearing one tank down soon and I'll put exactly the same soil and possibly the same plants because I have in excess and will see if I can reproduce a lowering TDS instead of a rising one. It would be handy instead of using RO water. I never kept soft water fish because I couldn't bother with RO but maybe I can now


----------



## NC10 (25 Apr 2014)

Ok mate, good luck with the new setup. 

Just a thought, but maybe if you didn't go with soil, they'd pull the magnesium/calcium out of the water even quicker?


----------



## sciencefiction (25 Apr 2014)

NC10 said:


> Ok mate, good luck with the new setup.
> 
> Just a thought, but maybe if you didn't go with soil, they'd pull the magnesium/calcium out of the water even quicker?




Thanks mate.
Why would a non-soil tank pull out Mg and Ca better? I've got 3 non-soils and they pull nothing out  I've got to do water changes to bring TDS down in them. That's what I've been trying to say and they are closed tanks.

Anyway, I am going with soil for sure, it just gives the best results, I'll see in a year 
I actually didn't intend not to do water changes, just had no time at all last few months so had to neglect some tanks.


----------



## NC10 (25 Apr 2014)

I just thought that if the only source of mg/ca was through the water column, it would obviously deplete/soften the water a lot quicker than if they had a secondary source to rely upon, like the soil. Plants need it and it's got to come from somewhere?? I don't know, said in my first I wasn't a scientist 

You really need to get yourself back into a water change routine anyway, save on all these dodgy TDS readings 

Good luck


----------



## sciencefiction (25 Apr 2014)

NC10 said:


> You really need to get yourself back into a water change routine anyway, save on all these dodgy TDS readings
> Good luck


 
Yeah, I think that's what I should have been doing. Glad my fish are still alive


----------



## sciencefiction (28 Apr 2014)

I think I know what caused the difference between the two soil tanks. I mentioned I used two different types of soils.

Well the tank with the low readings has verve fruit and vegetable planter as soil base. Just looked at the bag as I still have some left and it says 55%-60% peat like ingredients. It's a bugger because I didn't want to use soil with peat due to the clay I put in the soil but the tank has been perfectly fine.

The other tank has Homebase topsoil.


----------

