Using rainwater with low TDS, need to buffer?

[David R]

We're moving into our new house this weekend (which means I can start making serious plans for my next big tank!!!), I've just checked the tap water (which is collected on the roof and stored in a large plastic tank, and it is as follows;
ph: <6
KH; <20mg/L
GH; <60mg/L
TDS; eight. (yes 008!)
Ammonia/Nitrite/Nitrate; 0.

I'm planning a tank around 1800L with a mix of plecs (L190,L014,L128,L81), Geophagus, Black aro and a few other SA cichlids. Soft water is a nice problem to have with these fish. but I'm aware that such low TDS water can be devoid of all sorts of trace elements which can lead to problems for the fish later in life. At the moment the plecs and aro are in a 400L tank, and I've got plenty of old coral I can use to buffer the water to stop it from crashing with the large amounts of driftwood I have in the tank.

I know there are commercial buffers available, Seachem do a few different ones, but given the large volume of water I'd rather not be using off-the-shelf products that are fairly expensive here. Does anyone have any 'recipes' for trace elements that they dose when using rainwater or RO water? Or am I worrying about nothing, and the coral/driftwood combo will add enough "stuff" back into the water?

[dw1305]

Hi all,
You could buffer the water up with either oyster shell grit (sold as chick grit) or with coral sand (both are the more soluble aragonite form of calcium carbonate).

If you want to make a mix up, you can use calcium chloride dihydrate (sold for home-brewing), potassium or sodium (bi)carbonate (sold for cooking, you want potassium if you aim to have plants) and magnesium sulphate heptahydrate ("Epsom Salts" from the chemist). The fish should be able to obtain the nutrients they need from their food, so it would only be to add a small amount of dKH to stabilise pH. I would only go to 2 or 3 dGH/KH, and a TDS of about 50ppm (~ 100 - 120 microS conductivity).

The details you need for the re-mineralising salt are are here: <http://www.theplantedtank.co.uk/RO.htm>

cheers Darrel

[CUPfishhead]

I usually use one part marine salt, one part aquarium/rock salt, and one part epsom salt. I just watch my hardness and add accordingly depending on what you want your tds to be at. If you are going to be adding on a regular basis I would suggest that you spend the money and get a electronic tds meter that way you can have a better accuracy.

[krazyGeoff]

Hi David,
I have tried everything, all the seachem stuff, coral, oyster shell.
My water is softer than yours, but perhaps your test kits are more accurate than mine.
TDS of 60 which is a bit better.
At the moment I am on the aragonite buzz and than seems to be working well, but with the amount of water I change I think I just flush out most of the stuff I am putting in there.
I have a lot of schist in some of my tanks and I think that this may be playing a part in the mineralization formula?
Not a water scientist, of course, but scientifically curious
Cheers

Geoff

[David R]

Thanks, will look at link once we have internet sorted, hate browsing on my phone but it does help pass the time at work!

Geoff not sure how accurate the test kits are, they are just cheapo ones and I lost the glass vial for them so I'm using a different sized one and guesstimating the amount of water. The electronic tds meter should be accurate tho. Not sure how your water could be softer as mine is virtually undetectable, but I guess RO would have a slightly lower mineral content, is that what you're using?

I chucked a softball sized piece of coral in the sump and it seems to be doing the trick for now, will try experiment with adding salts etc once we're unpacked and sorted. For now the fish are happy, so I am happy!

[krazyGeoff]

Geoff not sure how accurate the test kits are, they are just cheapo ones and I lost the glass vial for them so I'm using a different sized one and guesstimating the amount of water. The electronic tds meter should be accurate tho. Not sure how your water could be softer as mine is virtually undetectable, but I guess RO would have a slightly lower mineral content, is that what you're using?

I can't detect GH or KH with the dropper tests.
Have a Hannah instruments TDS/uS/pH electronic meter for the TDS and pH.
Also have a bluelab pH meter and they are consistant.
Its just my tap water mate, hence my slightly higher TDS.
My pH starts higher than yours and I just have to make sure it doesn't crash too quickly, hence the previous efforts to stabilise the water. The resting point seems to be about pH 5.4

Cheers

[David R]

I found that my Auckland tap water was like that, despite coming from a different source to yours. High pH, very low khband gh, dropped very quickly in a tank with lots of wood.

[dw1305]

Hi all,

If you are going to be adding on a regular basis I would suggest that you spend the money and get a electronic tds meter that way you can have a better accuracy.

I'd definitely get a conductivity (TDS) meter, but I'm baffled by

one part marine salt, one part aquarium/rock salt, and one part epsom salt

How does it work? that is NaCl + traces, NaCl and MgSO4.7H20. No calcium, sodium chloride doesn't add dGH or dKH and no added dKH from the Epsom Salts. The high level of NaCl is why I would keep away from most commercial salt mixes, as I don't see any point in adding it, but again not every-one agrees <http://www.planetcatfish.com/forum/view ... =salt+NaCl>

I chucked a softball sized piece of coral in the sump and it seems to be doing the trick for now

This will work, the advantage of using a re-mineralising salt mix is that it is a bit more controllable, but there is nothing to stop using the coral, water changes and the TDS meter to keep your tank water stable and your fish in good condition. I'm lucky to have the advantage that I can use rain water and just cut it with a small amount of our hard tap water to keep the conductivity in the (80 - 120MicroS) range that I want.

cheers Darrel