I agree this mixture is on the threshold of solubility targeting 32mg/L Ca while looking at it with the solubility of CaCO₃ being 47mg/L equilibrium CO₂ @ 25c, however there is zero observable precipitation within the tank (water level evaporation precipitation excluded as its present but minor), that's not saying it doesn't happen though only that if it is happening it will be during the night CO₂ off gassing phase when the pH climbs toward equilibrium level of 7.8, reversing on the day phase with CO₂ injection down to pH6.2 (gas on 1.5hr before lights).
The water is pH monitored with calibrated probes (have 2 injected tanks using same source water, one with active substrate and one with inert gravel, the active substrate has near enough filled its CEC so the profile is only slightly different by 0.2pH points, the probes read the same exact figures they are supposed to when swapped around the tanks and when in both tanks together (to discount electrical interference), that's multipoint calibration in addition to two reference calibration fluids (4 and 7), the daily profile never changes and the atmospheric equilibrium point is always pH7.8 when read in the morning before injection phase, at water change the sample kept outside the tank for comparative analysis (where I store the probe to keep it wet while performing the change) always reads pH7.8 and the drop checker is always the same shade of green. It's the stable carbonate hardness, daily, weekly, monthly, that's important here for non variance pH controlled CO₂ injection in low conductivity waters (sub 200 TDS).
I should also say that I have a third tank that has the same water and also has active substrate (JBL shrimp soil) just red rams horns for fauna, mainly crypts and Java fern for flora, it has no CO₂ injection and very infrequent micro (macro front loaded in the water), Java fern not doing so well developing the shotgun blast look, crypts slowly doing well since they are planted and enjoy a little osmocote in the tropica powder soil base layer (JBL cap layer), the tiny smattering of duck weed on the surface is still green and multiplying (very very slowly thankfully), zero precipitation, Snails shells look great in this tank, not so much in the CO₂ injected tanks which look fairly shabby telling me day phase CO₂ injection leaves some room for the water to take up a smidgen more calcium robbing it over a long period of time mainly from the larger adult snails, although not enough to effect the water KH week to week.
The actual recipe for 25L water and further notes on preparation are as follows -
25L RO/DI water contained in a plastic construction tightly sealable Jerry can. The need for a tight seal is you want to retain the CO₂ in the overal mixture to keep CaCO₃ in solution for as long as possible, this also has an advantage that water changes and maintenance can be performed during the lights on phase of an injection cycle as overall the water in the sealed container roughly holds 30-35ppm CO₂ (this is what I have observed over quite a few months since using this remineralisation formula). Decant 900ml of this water to the soda stream bottle and refrigerate.
Add to 900ml Refrigerated Cold Carbonated RO/DI (one full level round in new type soda stream machine is enough)-
2g Calcium Carbonate
1g Magnesium Bicarbonate
0.25g Ascorbic Acid
In order to keep as much CO₂ from off gassing the above mixture is added to a food spice diffusion bag and placed fully and quickly into the neck of the briefly open bottle, above the cold pressurised water making sure to close the top tightly before shaking to mix (adding the powder without the bag can turn the water into a volcano, not quite bicarbonate into vinegar but it gets close). This mix goes back into the fridge for 24hrs just to give it time to go somewhat into solution, it's more of a suspension that can sediment but over 24hrs there is a massive reduction in sedimentation happening and the liquid takes on a cloudy lemonade look telling me some bicarbonate has formed, when the bottle is reagitated and the sedimentation goes back into suspension the resultant liquid looks like skimmed milk (importantly the mix has fully exited the spice bag by this time).
A day before performing the water change I will add to the 24.1L (or thereabouts water volume it may be more, I just need enough space in there to take the 900ml back and not spill over the lip when the Jerry can is sitting upright and level)-
1g Potassium Bicarbonate
0.75g Magnesium Nitrate
0.5g Magnesium Sulphate
0.2g Potassium Phosphate
Pinch of Magnesium Chloride
I don't measure the Magnesium Chloride out because it really is just a teeny tiny pinch just enough so Chloride is non-zero hence its magnesium content I don't add to the final numbers I'll give below.
Once these salts are in the water in the Jerry can I then take the cold bottle of bicarbonate/carbonate solution from the fridge and add it all in (opening the bottle slowly and no vigorous agitation beforehand as to not off gas too much CO₂), fish out the empty spice bag floating at the top and pour half the liquid into the Jerry can, the remaing liquid in the bottle is given a swirl around to pick up any sedimentation and poured directly into the Jerry can, I then seal the top and leave it overnight to go clear.
24hr dwell time for everything in the water is not any special number it's just the minimum time I have so far left it to sit before use and since I do two jerry cans at a time. The other end of the wait spectrum is a Jerry can sitting 2 weeks before use with CO₂ still being retained at 30-35ppm.
The resultant values in mg/L are (resultant water TDS <150) -
Ca / 32
Mg / 14.42 (not counting MgCl addition)
K / 17.9
NO₃ / 15
PO₄ / 5.58
S / 2.6
Cl / Non zero
GH / 7.8 (MgCl addition probably pushes this to nearer 8)
KH / 7.8
pH / 7.8 (@ atmospheric CO₂ from stored sample which correlates with in tank behaviour)
In tank CO₂ injection phase behaviour -
pH / 6.2 (estimated 30ppm CO₂ via Lime Green colour change to Drop Checker 4dKH sample)
I have not measured the pH directly in the Jerry can but performing a water change (50%ish of total system water, 80%ish tank volume which other than plants there's is only 10 year old Bogwood and inert gravel substrate to alter the water chemistry to which it doesn't), the resultant refilled tank pH is 6.1 (controller set to 6.2 so once the canister filter is restarted and left to run for a few minutes the excess gasses off quickly and the controller can kick in when it reaches its control point).
Zero issues (inspecting for sedimentation issues within the Jerry can before use and there are none), crystal clear water. Further to this I'm currently skipping a water change or two to test if the KH drops over a longer period between water changes, 3 weeks so far and the KH hasn't budged (CO₂ equilibrium point is still pH 7.8 and the CO₂ addition pH drop to 6.2 results in the familiar lime green drop checker), micro daily and bio carbon every two days (non chelated micro, only chelation is if it binds with any free Gluconate that the Iron is sourced from when mixed in the same bottle).
For interest my daily micro dose levels in mg/L are -
Fe Gluconate / 0.1
Fe DTPA / 0.05
Mn / 0.05
B / 0.03
Cu / 0.002
Mo / 0.0015
Ni / 0.0005
The motivation for all this was trying to get Bucephalandra to thrive without deficiencies (leaf holes, curled malformed leaves, melt), previous remineralisation strategies were first Salty Shrimp Bee GH+ for 0KH, the rhizomes didn't appear to like this and disintegrated, I'm speculating through super low pH causing beneficial rhizobacterial colonies to not thrive, EI with FeEDTA based micro, stem plants absolutely thrived here. Next stop a combination of Salty Shrimp Bee GH+ and Seachem Alkaline Buffer (to KH8), brought the pH right up averaging neutral between CO₂ injected and degassed pH, halted rhizome degradation but any growth was glacial with curled malformed tiny new leaves, pinholes in old growth worst affected would melt in half if lucky, unlucky if the whole plant melted, grim if it's a whole bunch. Worried about iron dropping out of the EDTA I added supplemental FeDTPA, issues remained. I was providing all the necessary nutrients but no improvement. Stopped using Alkaline Buffer as I ran out and couldn't justify the cost of it (being mostly sodium bicarbonate) and swapped it out to Potassium Bicarbonate for the KH (that's a load of potassium before accounting for what comes along with the nitrate), not long after this did I stop using EDTA derived micro (ruminating that I may have FeEDTA de-chelation issues) I swapped to making a mix of Seachem Trace with Flourish Comprehensive (to near EI levels) fortified with Fe DTPA, got growth but leaf issues persisted, melting stopped though. Stopped using Seachem Trace (dosed at EI levels it gets expensive fast) and went DIY, went the whole hog and rethought the whole process for remineralisation focusing on Tap waters from natural sources where others (Vasteq mainly since he appears to have nailed it) had success with these plants and was compatible with CO₂ injection in mind. The above is the result.
I can now grow Bucephalandra. No melt. No disintegrating rhizomes. No malformed or tiny new growth. No pinholes. It's a minor victory but I'll take it.
Where there's growth (1 leaf every two weeks on the strongest growing plants) the Rhizome is elongating and new leaves reach maturity normally without deficiencies. Their mass is increasing. Current skipping WC test showed halted growth in new leaves after second week, phosphate or nitrate likely bottomed out a bit (still feeding fish in here) and it's readdition got growth going again, halted leaf has now opened growing again (without malformation) and a new leaf is on its way.
Read lots, learnt lots, thankfully now reaping the benefits.
It's my Cat and this is how I skin it!
