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The ro unit is a week old, i didn't get D.I fitted to it as i didn't see the need for it with freshwater, the unit is from RO Man.
The water straight from the unit (after discarding 10g) was; ph pen - 5.5 / ph test kit - 6.0, kh - 0, gh - 0, and a tds of 5.

I asked because when my RO was new it was producing quite alkaline water due, i think, to the preservation fluid that the membrane came in. Yours seems fine though.

I use a A.P.I. test kit for kh, what test kit do you use to get a reading of 1.68 ?

I use the Nutrafin kit, and the seemingly precise 1.68 reading is just due to the maths involved (3 drops x 10 x 0.056 = 1.68dKH).

Why dos my waters ph shoot up so much when i try to buffer it, when i read of people who have reasonably soft water but decent buffering ?

Simply because you are buffering it too much; a buffer is just an alkali to neutralise the acid. More buffer = more alkaline. The chemical balance of the fishtank is far to complicated too prescribe a solution to everyone, as all buffers are different in their properties, and other chemicals interact with them and confuse the situation (like tannins and phosphates). Just mix your water up to 1-2 dKH and keep testing your tank, not the water in your storage vat, as it is too unstable there. If at any point it dips lower than you would like, just mix up a slightly stronger KH solution in your vat for the next water change, and use that from then on.

Always read it is best to have sand in a pl*co tank, but do you think a thin layer of pea gravel would be alright,

I would always use sand, as minute particles of food can get trapped in the gravel, and loricariid fry are very sensitive to this. I don't see the value in using gravel, even with regular cleaning.

Thanks Racoll for answering all the questions, it has helped a lot and cleared up some things i had been wondering about for a while.

I will need to get another ph pen, don't trust them if they seem to be acting up, ro man has a couple on his web site, just need to store it better.
Ordered a new phosphate test kit, just to check if the ro unit is clearing all the phosphate out of the my tap water.

AndrewC wrote: to check if the ro unit is clearing all the phosphate out of the my tap water.

From a chemist's point of view, I wonder what might be yout tds - I mean, I know it is total dissolved solids, but I wonder what is dissolved.

I don't expect any phosphate in this water, if any is in it, your RO unit would be broken - and you wrote it is brand new

Bas Pels wrote:

AndrewC wrote: to check if the ro unit is clearing all the phosphate out of the my tap water.

From a chemist's point of view, I wonder what might be yout tds - I mean, I know it is total dissolved solids, but I wonder what is dissolved.

I don't expect any phosphate in this water, if any is in it, your RO unit would be broken - and you wrote it is brand new

It`s the oxonium-ion H3O+ (often just called H+) from the protolyse by the ...phosphat he has in his tapwater. TDS meters are exactly coductivity meters (Leitfähigkeitsmessgerät in German, Google translater tells me: Geleidbaarheidsmeter in Dutch), they measure not how much salt is in the water they measure how much conductivity you have. And conductivity is much more given by H3O+ and OH- as from salts. What makes it bullshit to talk about TDS when you use them That I say from my water-chemical point of view

You could very well be right. I did not know a tds meter measures conductivity

Bas Pels wrote:

AndrewC wrote: to check if the ro unit is clearing all the phosphate out of the my tap water.

From a chemist's point of view, I wonder what might be yout tds - I mean, I know it is total dissolved solids, but I wonder what is dissolved.

I don't expect any phosphate in this water, if any is in it, your RO unit would be broken - and you wrote it is brand new

I will be checking the storage tanks but expect a zero reading, and will be testing some tanks to see what phosphate reading they have.

they measure not how much salt is in the water they measure how much conductivity you have. And conductivity is much more given by H3O+ and OH- as from salts. What makes it bullshit to talk about TDS when you use them

You could very well be right. I did not know a tds meter measures conductivity

Are you sure hydroxides and hydronium contribute towards conductivity?

The conductivity (microsiemens per centimetre or µs/cm) is a measure for the concentration of the dissolved salts in the water. These salts include all the common ones that affect water hardness including calcium, magnesium, potassium and sodium as well as any trace elements. TDS as measured in mg/l or ppm is just conductivity multiplied by two, and is a proxy of concentration.

They don't give you a complete 100% accurate chemical breakdown of the water, but what do you expect for £50?

racoll wrote:Are you sure hydroxides and hydronium contribute towards conductivity?

I certainly do.

Most likely, your reaction is based on a line of thought like "at pH 7 only 10 exp -7 of eaxch is around, thids is so little,it can be neglected'. At pH 5 the H3O+ os 10 exp -5, but the OH- is 10 exp -9,

10exp-7 *1- exp-7 = 10 exp-14, just as 10 exp-5 * 10exp-9. In both cases the total cunductivity based on ordinarily ion movement (just as Na+ and Cl- and so on) would, indeed, contribute to nearly nothing.

HOWEVER

Water is a very strange, intersting stuff, in fact it is the most weird thing I know

In water, the watermolecules, H2O, are all conected to each other. The oxygen atom has two spots on it, where they concentrate their negetive charge. Further, even in a molecule, the H is quite positive.

+ attracts -, and thus the O attracts H - apart from the 2 it is bound with.

The bounding can be replaced, and in reality, the bounds keep changing very fast indeed.

Using this system, no molecule needs te be replaced to transport electrical charge, only bounds need to be reconnected - which goes very fast.

If someone would like to do the test:

1 take demineralised (or RO) water - as pure as possible - measure the condutivity

devide the water in two, and add a certain amount of NaCl - say 1 mmol a liter to one part
add a similar amount of hydrochloric acid (HCl) to the other part - so, that the concentration is the same.

measure the conductivity for both.

As both have the same amount of charge carriers, one would expect the same conductivity (try a third batch, with potassium bromide, for instance, as these ions are larger, a slightly , but perhaps not measurable, lower condictivity will result)

The difference comes from the above introduced system

racoll wrote:Are you sure hydroxides and hydronium contribute towards conductivity?

Sure, I saw it at different experiments. The one you sould try after that from Bas Pels is to take 150ml RO water and put 20ml 0,1M HCl and your TDS meter in, then you supply succrssive 1ml 0,1M NaOH till you have 40ml 0,1M NaOH inside. This way you will see that first your TDS will go down (think you have now more salt dissolved) till 20ml, from then it will go up.

racoll wrote:TDS as measured in mg/l or ppm is just conductivity multiplied by two

What makes it that worse As there is no reason to do so

racoll wrote:They don't give you a complete 100% accurate chemical breakdown of the water, but what do you expect for £50?

Nothing As far as only TDS is shown.

Thanks for your replies Bas and Durlanger, but what implications does this have for the aquarist?

Well, we should speak about conductivity instead of TDS.

Back to topic
- we still have Jools Oyster Sheels as softest = best methode for the normal aquarist (for example AndrewC)to use inside the tank
- then I would say the next stronger methode would be supplying little ammount of NaHCO3 to tape water befor using RO unit, something for the aquarist with chemical background (like Bas Pels)
- then I would say the very next stronger methode would be supplying little ammount of Na2CO3 to tape water befor using RO unit, again something for the aquarist with chemical background
- I wouldn`t use stronger methodes as those mentioned

Durlänger wrote: Back to topic
- we still have Jools Oyster Sheels as softest = best methode for the normal aquarist (for example AndrewC)to use inside the tank

I have a few tanks, some with cannister filters, some with internal power filters (Fluvals) and some with sponge filters, half are 20g in size & the other half are 30g.
I can only think of; putting one shell in each tank, or a piece of shell in each tank, or a few shells in a media bag into each tank, which then dissolve slowly, buffering the water.
Is the only way to judge the amount of shells needed for each tank and how they affect my water, to put a shell in a bucket of my water, and test the bucket regularly over a few weeks ?
And do all the shells dissolve at the same rate and give off the same amount of buffering, or would i be checking each tank every couple of days ?
Oyster shells do sound a good idea, but sound better for one or two tanks which are easier to keep an eye on, rather than a few tanks, or am i wrong ?

As a very rough guide, I use 1 oyster or 2-3 mussel shells per square foot. There isn't a lot of science to it. They will last for 8-14 months depending on water change regime. They don't raise pH, they simply avoid crashes.

Jools

Jools wrote:As a very rough guide, I use 1 oyster or 2-3 mussel shells per square foot. There isn't a lot of science to it. They will last for 8-14 months depending on water change regime. They don't raise pH, they simply avoid crashes.
Jools

Thanks Jools
Checking a tank one day and finding the ph raised a lot is what i was worrying about, so for a 24"*18" tank, 1 oyster shell would be alright, and for a 32"*18" tank, 1.5 oyster shells would alright.
I like the idea of oyster shells/ mussel shells the more i here about them, but will need to source them out online.
Are the shells on this link from a Online Koi Shop, the same size as the ones you use http://www.koi-fish.co.uk/acatalog/koi_ ... media.html, they are the fourth item on the link.

racoll wrote:Thanks for your replies Bas and Durlanger, but what implications does this have for the aquarist?

I think one should mention pH when referring to any conductivity

AndrewC wrote:Are the shells on this link from a Online Koi Shop, the same size as the ones you use http://www.koi-fish.co.uk/acatalog/koi_ ... media.html, they are the fourth item on the link.

I take them home from restaurants (or get given them by friends who also know my weird need) but it's the same thing as in the link. Find a restaurant that sells oysters, go and have a quick word with the chef and you'll either get them free (it's recycling after all) or they'll cost you a six pack of beer... Plus if they are fresh(ish) you can rinse them and let the fish pick the last of the oyster flesh from them.

Jools

Bas Pels wrote:

racoll wrote:Thanks for your replies Bas and Durlanger, but what implications does this have for the aquarist?

I think one should mention pH when referring to any conductivity

This has been an interesting read.
I think conductivity/TDS readings are not very meaningful unless taken in a known context.
For example; I do not use any RO additives normally. I maintain a current report of our local water supply's EPA required analysis but it doesn't vary significantly as our water is all from the same deep well. I see that the electrolyte balance is pretty good so I can usually achieve any target lower than the tap water by mixing it with RO in varying ratios. Since I know my starting point. a TDS reading is a fair indicator of any water so adjusted. Of course the pH is a separate parameter but very few soft water fish require a pH lower than 5.5 which I can achieve using only peat filtration and nearly straight RO water.

Without a fairly complete analysis of the water, neither TDS nor electroconductivity readings tells you what species of chemicals nor what their proportions are. There is a general relationship between TDS/electroconductivity and they are interchangeable to me provided I know what the full analysis of the water is.

That pure water should have some conductivity even with no TDS makes sense enough to me that I would not like to be standing in a tub of pure water with 220 volt household current applied to it. The polarity and constant flux of pure water molecules is taught in high school chemistry and that an induced direct current in pure water will split water molecules into elemental H->H2 and O->O2. If pure water wasn't conductive how else could the electricity electrolysize it into O2 and H2?
I am no chemist and this post probably makes that obvious but I do appreciate just what a strange substance water is and discussing its properties is a complex subject.

I would love to have water out of the tap with a KH of >2. If nothing else, it ought to give one a bit more RO membrane mileage.