# Perfect water for plant growth (hypothetically at least)



## alan'67 (13 Dec 2016)

Having read an awful lot of great info on this site from some very experienced plant growers, I've found myself in the situation where I seem to have read loads but seam to be none the wiser!.

As an example, I would like to ask what would be the ideal water parameters in the following scenario:

There are three identical tanks, all the same size with the same lights, substrate, co2, plants and using EI ferts regime with EDTA dry salts.  

Tank A use's 100% RO water, PH 7.

Tank B use's 100% Tap water with a GH of 18 & a KH of 11, PH 7.8.

Tank C use's a mix of RO and tap water to get a GH of 5 and a KH of 3, PH 7.2.

Tank A.
As RO water is free of all carbonates I believe it is unsuitable to grow plants because it has been stripped of all essential nutrients that plants need. Plus, it is prone to rapid PH swings because the lack of alkalinity of RO water effects its ability to resist (buffer) Co2 gas absorption.  

Tank B.
Better in terms of it's ability to provide a source of calcium/carbonates to plants, plus the alkalinity helps 'buffer' against rapid PH swings?.
The major drawback is even with high co2 injection,the PH is unlikely to drop below 7 without gassing your critters.
This will directly effect the EDTA Chelator used in micro ferts making them unavailable to plants.
The EDTA chelator is only effective on a PH lower than 7.

Tank C.
Err, sounds about perfect!

Is the above right? or do I need to read a bit more!


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## ian_m (13 Dec 2016)

The perfect water is the water that comes out of your tap. Costs about 0.3p per litre. May also contain essential minerals for the plants, calcium, nitrate and if lucky some phosphate.

Using this is easy, compared to using RO, remineralising RO, RO costing approximately 3p per litre and all the faffing needed to use RO.

So perfect water is the water you have got on tap.


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## dw1305 (13 Dec 2016)

Hi all,





ian_m said:


> The perfect water is the water that comes out of your tap


 I agree, or for me out of the sky as rain-water. 





alan'67 said:


> Tank A use's 100% RO water, PH 7.


The pH will be about pH5 because of the dissolved CO2 (as H2CO3).





alan'67 said:


> As RO water is free of all carbonates I believe it is unsuitable to grow plants because it has been stripped of all essential nutrients that plants need. Plus, it is prone to rapid PH swings because the lack of alkalinity of RO water effects its ability to resist (buffer) Co2 gas absorption.


If you use 100% RO you could change your EI mix to include potassium carbonate (K2CO3), or bi-carbonate (KHCO3), as the potassium source (and source of dKH).  Once ions are in solution it doesn't matter what compound they came from. Most people who use RO have hard (CaCO3 rich) tap water, so they can just cut their RO with 10% tap to give both some dGH & dKH.

There are plenty of plants from very soft water that only thrive at low dKH, but they tend to be more specialist (_Eriocaulon, Tonina_ spp.) etc.

I used to make up hydroponic growing solutions without one of the essential nutrients. These are for looking at plant deficiencies, in which case you start with RO and then add everything else plants need other than the missing element.

You have to use analytical grade salts, or otherwise you tend to get micro-element contamination.  If you ignore the macro-elements, the easiest deficiency symptoms to induce are magnesium deficiency, where plants will grow with a trace amount, but show deficiency symptoms. When you add some magnesium you get an almost instant greening and growth.

We used to use <"perlite trough culture"> for these experiments, partially because the presence, or absence, and colour of green algae on the perlite surface gives you a good idea about the nutrient status of the pot. 





alan'67 said:


> Plus, it is prone to rapid PH swings because the lack of alkalinity of RO water effects its ability to resist (buffer) Co2 gas absorption.


 You can ignore the pH swings in water without any many salts.





alan'67 said:


> Tank B use's 100% Tap water with a GH of 18 & a KH of 11, PH 7.8.


It depends on the plants, if you go and look at a chalk stream in the UK it will have plenty of plants in it. Plants like _Vallisneria americana, Ceratophyllum demersum or Cryptocoryne crispulata balansae _naturally grow in alkaline water, and can use HCO3- as a calcium source, are very efficient at sequestering iron (Fe++) ions etc. EDTA is fine as a chelating agent for a lot of plants, even in hard water. 

Have a look at "@akwascapes" low tech <"Windowsill Nature"> tank. 





alan'67 said:


> Tank C use's a mix of RO and tap water to get a GH of 5 and a KH of 3, PH 7.2


A lot of people who use RO do this, the pH will actually still be ~pH8 because of the dKH~ pH ~ CO2 equilibrium, but you won't have much dKH buffering.

I use a similar approach with the rain-water I use, I don't worry too much about pH, but when the rain-water is very soft in the winter I add a bit more tap (~17dKH) to keep the conductivity above 100 microS.

cheers Darrel


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## alan'67 (14 Dec 2016)

Thanks for the info guys, akwascapes tank does indeed look superb that's for sure.

Just a couple more questions if possible.

Firstly, I have tap water like Tank B, so it's hard with high alkalinity. I've never measured it but will that mean this water will always have a high TDS reading?.

If this is correct, will that effect the plants ability to absorb micros in the water column?.

Is the amount of Total dissolved solids in your tank of no importance at all?.

Being new to planted tanks & having hard water, I tried on two occasions with vallis as I believed it was ideal for my tap water. Both times the plant failed to grow and eventually melted away.
Could my tap water still be lacking something even though this plant should have been ideal in my tank?.

Also, in your opinion, if there is no advantage to using RO water why do you think so many aquascapers  use it?.

actually, that's more than a couple of questions!.

Sorry about that.

Thanks.


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## ian_m (14 Dec 2016)

alan'67 said:


> Also, in your opinion, if there is no advantage to using RO water why do you think so many aquascapers use it?.


Because
- They can control the water parameters exactly.
- They are growing "difficult" plants.
- They have sensitive fish. Some fish only spawn in soft water.
- Don't like lime scale on their rimless open top tanks.
- They can afford it.
- They love high tech gadgets...



alan'67 said:


> Both times the plant failed to grow and eventually melted away.


Melting and plant mechanical issues is generally a sign of lack of carbon for the light levels you are providing. Also can be caused by liquid carbon. Some plants are not happy with liquid carbon and just melt away.

See this link for plants growing absolutely perfectly in hard water.
https://www.ukaps.org/forum/threads/high-cec-with-hard-water-pointless.38582/#post-418921


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## dw1305 (14 Dec 2016)

Hi all, 





alan'67 said:


> I've never measured it but will that mean this water will always have a high TDS reading?.


Yes it will. The actual value will vary a bit with temperature (because of the CO2 solubility), but it is never going to fall below about 300ppm TDS (450 microS).





alan'67 said:


> If this is correct, will that effect the plants ability to absorb micros in the water column?.


Yes it will for some nutrients, but it depends on the plants. 

Plants that naturally grow submersed in alkaline waters will be very efficient at sequestering the very low levels of  iron etc that occur in the water they evolved in.

It is difficult to keep iron (Fe+++) in solution as will form insoluble iron hydroxides, phosphates and carbonates. This is why we use a chelator like EDTA.  



 

It also effects the proportion of dissolved inorganic carbon (TIC) that is CO2. (From <"https://www.ukaps.org/forum/threads/aquasoil-ph-increase.41555/">). Obligate aquatic plants from hard water will be able to utilise HCO3- as their carbon source.





alan'67 said:


> Is the amount of Total dissolved solids in your tank of no importance at all?.


No not really. If you have hard water some plants (_Vallisneria, Ceratophyllum demersum_ etc) and fish (Live bearers, Rift Lake Cichlids) do better, and others struggle (_Tonina, Apistogramma etc._). 

Have a look at <"In praise of hard water">.

cheers Darrel


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## alan'67 (14 Dec 2016)

Thanks Ian & Darrel for taking time to reply to my questions & posting those links, much appreciated.

Your replies and the links you provided have raised a few more questions though!.

If my TDS is already about 300ppm from the tap, what would happen if I dose dry salts to the recommended EI level?. Do you know at what level my TDS would end up and could this become an issue?.

Also I noticed akwascapes  superb tank looks like the Walstad  type, using soil capped by an inert gravel.

Is it vital to separate a soil substrate from the water column with a cap to stop excessive organics/nutrients leeching into the water column?.

I have seen the videos on the Tropica website and they often cap the Tropica soil with either sand or gravel.

Apart from aesthetics, does capping soil help plant growth?, will using an 'all in one soil' uncapped raise my TDS even more?.

Would it be a good idea to put a covering layer over the soil when it starts to age/fall apart a bit?.

Thank you.


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## dw1305 (15 Dec 2016)

Hi all,


alan'67 said:


> If my TDS is already about 300ppm from the tap, what would happen if I dose dry salts to the recommended EI level?. Do you know at what level my TDS would end up and could this become an issue?.


The suggestion would be that for most fish TDS doesn't become an issue until you are in the thousands.  This is a very good water quality article that looks at TDS. <"Water Chemistry: Osmoregulation, Ionic Imbalance & pH"> by Joe Gargas.


alan'67 said:


> Is it vital to separate a soil substrate from the water column with a cap to stop excessive organics/nutrients leeching into the water column?.


It isn't really nutrients, the problem is the soil is really easily stirred up if you don't have a cap, and you end up with sediment on the plants and cloudy water.

The main problem with capping light media is that it tends to end up on top of the denser capping material. I have a couple of tanks where I used 90% sand and 10% gravel as a substrate (plus a very small amount of clay and leaf-mould).

I made the <"sand and gravel mix for a high flow tank">, where I expected the flow to sort the sand and gravel into discrete areas fairly naturally.

I used the left over, but what I found in a "normal tank" was that over time the gravel all ended up on top of the sand, possibly because of the MTS.

cheers Darrel


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## alan'67 (17 Dec 2016)

Cheers for the info Darrel and providing that link, at least TDS is one less thing to be concerned with.

I belive I might be over thinking things some what!.

I thought capping substrate helped with bacteria development and had a stabilising effect on nutrient exchange between EI dosing and what the plants roots can handle.

Thanks for the help.


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## dw1305 (17 Dec 2016)

Hi all,





alan'67 said:


> I thought capping substrate helped with bacteria development and had a stabilising effect on nutrient exchange between EI dosing and what the plants roots can handle.


It might have some effects, but you would still get nutrient exchange between the substrate and the water. 

I'm not sure many people will have kept a non-capped soil based tank, so comparisons between "capped" and "non-capped" are possibly difficult to find.  

cheers Darrel


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## xim (17 Jan 2017)

alan'67 said:


> I have seen the videos on the Tropica website and they often cap the Tropica soil with either sand or gravel.
> 
> Apart from aesthetics, does capping soil help plant growth?, will using an 'all in one soil' uncapped raise my TDS even more?.



I think you may be confusing two of their products.

Aquarium Soil: http://tropica.com/en/plant-care/aquarium-soil/aquarium-soil/
No capping is required for this one.

Plant Growth Substrate: http://tropica.com/en/plant-care/substrate/
This one (as they say) needs capping.



alan'67 said:


> Would it be a good idea to put a covering layer over the soil when it starts to age/fall apart a bit?.



When this happens to a high tech tank (using baked/fired clay substrate without capping), people change all the soil or remove some then add new soil to cover it.


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