Water returns to initial hardness after distilled water change?

Hi, we wanted to lower our KH from 7° to 4°, to accomodate Bee shrimps before adding them.
To do this gradually, we decided to do our weekly 30% water change with 2/3 distilled water, which unfortunately dropped KH and GH by 2° instantly after the water change.
Thankfully everyone in the tank seemed to be doing fine, however two days later, KH and GH are back to where they were before.

Is it normal for the hardness to recover like this, and if so how can you reduce the hardness with distilled water?
If the Bee shrimp seem to be active and acting normally in 7dkh, do we really need to decrease hardness if we don't mind them not breeding?
If distilled water doesn't work, should we try using Seachem Acid Buffer?

We are also considering trying peat, as we don't want to get and RO unit and the rain water is probably too polluted.

The parameters have been stable at GH: 8°; KH: 7°; PH: 8; NH3/NH4, NO2: 0; NO3: ~3mg/L
Our tank is a planted 20L (5Gal) with Tropica substrate, we have a Betta, 9 Least Rasboras, 10 Cherry shrimps, and we just got 10 Bee shrimps, everyone seems to be doing good.

https://imgur.com/b84w6Dz

 

That's an indication that something is dissolving out of your substrate or decorations.

it's pretty common.

 

Thanks Truckjohn, so I assume this means that reducing the hardness using distilled water is ineffective.
Would using an acid buffer or peat possibly result in a more durable solution?

 

Croeso welcome to fishlore.Where your gh & ph are ok for cherries it's not so for bees, those caradina are more suited to RO or distilled water reminerilised to specific perameters, if you drip acclimated them there's a possibility they will live if not they're living on a fine line, if they do live they won't breed, its a beautiful looking tank and more suited to cherries but small tanks like this are very hard to get stability. The rocks are probably leaching minerals which raise TDS & GH,
The ideal perameters for bees are TDS130 GH4 or5 KH3, If you can get your perameters to this both caradina & neocaradina will live and breed albeit slower as I was doing it but have now separated them. You also have to consider the best needs for your fish, whatever you do I hope it works for you

 

Thank you very much richie.p for the extensive description! I have indeed drip acclimated them, and based on people managing to maintain low hardness and TDS through distilled WCs, I throught caridinas were worth a try based on how stable our parameters have been with good NO and NH levels. I would like to offer them better conditions however, that's why I was aiming to decrease both KH and GH by 2-3 degrees at least, and will test the TDS next week.
Do you have experience with decreasing hardness using the acid buffer or peat by any chance?

 

Thank you very much richie.p for the extensive description! I have indeed drip acclimated them, and based on people managing to maintain low hardness and TDS through distilled WCs, I throught caridinas were worth a try based on how stable our parameters have been with good NO and NH levels. I would like to offer them better conditions however, that's why I was aiming to decrease both KH and GH by 2-3 degrees at least, and will test the TDS next week.
Do you have experience with decreasing hardness using the acid buffer or peat by any chance?

I wish you all the luck with this, I cheat when it comes to water all my tanks are RO water and reminerilisde to what I need I use a substrait that keeps my ph at 6.5, by the time you've finished you'll have more practical experience than I do with small tanks, I've never used peat. Once you get your gh to 5 hold it there as I know from experience both cherries and bees will survive and breed, go any lower than gh5 and you'll see cherries with moult problems, as you are they will both live but the bees won't breed for you

 

The suggestion of substrate or decor is pertinent, what is in your tank apart from the Tropica substrate? I have a bit of that in my tanks, contained in pots or mesh bags, and haven't found it to affect the water parameters but an entire substrate may. On the other hand plants reduce KH by consuming CO2. I have the same issue of soft water fish in a hard water area - it tends to come out of the tap PH 7.8, KH 9, GH 17 which is not ideal for my fish, I also have bettas in a specialist community. As stated above I have found using RO and re-mineralising with buffer (I use Aquadur) to be effective and almond leaves also help lower PH and KH a great deal along with their other benefits. Stable is good so adjusting these parameters is always risky. I tend to mix a % of tap and RO water - I wok out a predicted drop in PH, KH, and GH and calculate % of mix and amount of re-mineralisation if any for that water change. dropping PH by 0.1 or 0.2 seems ok with a drop of 2 or 3 KH and GH at a time seems ok but I also would appreciate feedback on this. I got nerdy and did this sheet which might help - first page is for my two freshwater communities, second is marine so only the first is relevant here. The formula for calculating predicted drops and how much I any re-mineralisation is needed is a little fiddly, can type it out if you're interested.

 

Thank you richie.p! AZL we have an entire substrate of the Tropica, some generic black aquarium gravel with some generic white gravel for the path, I'm assuming these are neutral. The main suspects for the hardness are the large grey decoration stones, which had a minor and short reaction with vinegar, however the stones we used to fix the moss were completely neutral. I'm also assuming the drift wood decreases the hardness. Of course we have extensively boiled everything both with and without salt before putting them in. We already have some almond leaves in the tank, but they haven't had a noticeable influence. Thanks a lot for the sheet, however I think we'll probably have to experiment with peat first to see whether it's a more durable solution than water changes.

 

I've yet to try peat myself, still researching and asking around and I'll pass on what I hear or experience. Actually a friend at the other LFS brought it to my attention that peat is not a renewable resource so there are environment issues with using it, apparently sphagnum is a good substitute. I put at least 1 leaf per 10 litres in and make 'tea' with them first which also goes in when cooled down mixed with cooler water to achieve the correct temperature. I've seen a lot of info on alder cones being even more effective so am going to try them soon as well. As far as added prepared water to tap water to lower PH and hardness distilled water is neutral at 7 and does possess some mineral hardness. RO water comes out 7 but drops to well below when exposed to air so more effective at lowering PH in water but requires care and caution to avoid an abrupt drop. Also if not re-mineralised it will lower hardness - once the correct hardness is achieved it needs to be re-mineralised to maintain that as KH getting too low is dangerous for even soft water loving fish. Very tricky stuff, I'm just trying to wrap my head around it all and find the best way forward as well!