RO Remineralising Quanitites in Nano Tank

SilverB

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Hi All

I've recently set up my 20 litre, planted nano tank. I've elected to use 100% RO water which I am remineralsing, and I wanted to ask if others have done this and how they scaled their doses for various quantities of water for a nano tank, i.e. large quantity at start up, 50% water changes and 20% water changes and so on.

I'm using Seachem Replenish, Seachem Acid Buffer and Seachem Alkaline Buffer, with the aim of attaining the following water chemistry: dGH 1 (2.5ml per 20litres), pH 6.5 (Acid Buffer 1.2g per 20litres & Alkaline Buffer 1.5g per 20 litres).

In order to scale the doses down, with Acid Buffer as an example for a 50% water change of 10 litres:
1.2g/20litres = 0.06g per litre x 10 = 0.60g

I have observed however that my dGH is sitting between 5.4-6.4 which is much harder than I was aiming for.

I don't know where I should expect KH to be based on the Buffers (as Seachem aim for pH rather than a KH reading) but it's sitting at around 3 when the water is mixed and drops to 2 in the tank after about a day (though sometimes freshly mixed water is reading as 2). I expect the KH to go down in the tank as I'm also using Tropica soil which has some buffering capability. Is there a converter for KH vs pH? I'm assuming not since the KH is just to stabilise the pH, not create it.

My pH is stable and generally reads at 7 though sometimes it looks a bit more orange than red so I expect its sitting between 6.5 and 7.

Bottom line, is it normal to see some mild fluctuation?
Should I be scaling my quantities the way that I currently am or is there a more accurate way to do this?

And lastly, should I be overly concerned? The tank has been set up for a week and 2 days and I plan to stock 6 Chili Rasbora (though it currently seems better suited for shrimp!)

If helpful, since set up:
Daily 50% water changes for the first week (no ferts)
Alternate Day 20% water changes for second week (ferts)
Will aim to drop to either weekly 20% water changes or bi-weekly 10% water changes (ferts)
Light is on 6 hours for first 3 weeks, to then increase to 8 hours
Tank is heavily planted with all easy grade plants including; Anubias, Spikey Moss, Bacopa, Crypts and Sagittaria
Hardscape: Lava Rock, Wood (not sure which type honestly), sand and Tropica Soil

Cheers in advance!
 
Bottom line, is it normal to see some mild fluctuation?
Should I be scaling my quantities the way that I currently am or is there a more accurate way to do this?
yes you will normally see some fluctuations. They can be of concern depending on why the change occurred.

Replenish is mainly made form calcium chloride and magnesium chloride. Plants and fish need all 3 but plants need a lot more calcium and magnesium and very little chloride. So as the plant grows excess chloride will accumulate in the water. This will push the PH down and reduce KH. GH will drop but most test kits have a resolution of 1 degree. Typically not enough to see the GHdrop.

Note other GH boosters on the market use calcium and magnesium sulfate and sulfates are widely used in fertilizers . Plants also need sulfates so sulfate GH boosters will also have the same effect on PH, KH, and GH.

In my 20L 100% RO water tank I use a gh booster and a sea shell in my filter. No buffers. The sea shell is mainly solid calcium and magnesium carbonate (crushed coral, and limestone are also Ca Mg carbonates). Calcium and magnesium carbonates only dissolve in water when the PH is less than 7 it doesn't dissolve when the PH is above 7. So my KH levels are very low. But my PH stay very close to 7. At normal light levels I see a PH of about 6.7 light off with a PH of 7.3 lights on. If I turn up the light the PH increase is larger. Once the lights turn off the PH drops quickly back to about 6.7. This PH fluctuation does not appear to affect my blue dream shrimp in any way.

Note that using 100% RO water causes some challenges with fertilizers. Many fertilizer manufactures reduce nutrients plants need if those nutrients are commonly present in tap water (typically calcium, magnesium, copper, and zinc. I couldn't get consistent plant growth with 3 fertilizers I tried. I would strongly advise you too try and mix in some tap water in with your RO water.

After failing with purchased fertilizer I decided to make my own. That in itself is challenging but I managed it. I have since learned of one fertilizer that has similar nutrient levels to what I use and that fertilizer is TNC fertilizer.It is not available in the US but it is available in the UK. You will still need a GH booster.
Sldo in my opinion 20% water changes is too small in my opinion. I do 50% once a week.
 

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