My tap-water is way harder than my tank-water and I'm killing my shrimp after every water change

[freshwater_hedgehog]

I have a 20 gallon heavily planted aquarium with fluval stratum substrate and some driftwood. The plants/fish/cycle is doing great (ammonia and nitrite are 0 and nitrate = 5). I have a trio of guppies, a scarlet badis, and a pair of killifish. The tank has been setup for several months.

The problem is my GH/KH. When I test my tapwater I get:
GH = 50 ppm
KH = 200 ppm
pH = 7.5.

When I test the tank I get:
GH = 25 ppm
KH = 20 ppm
pH = 6.5.

(My test strips aren't the best so these are rough numbers only. Better strips are in the mail).

So the tapwater is drastically harder than the tankwater. Its been like this since setup after several months of weekly 10% water changes. I've tried to keep amano and cherry shrimp but a few die after every water change. I've resorted to very slowly dripping in water after a water change over 6-8 hours so avoid large changes but I'm guessing this isn't ideal? Should I try RO water and remineralize? should I try to find a ratio of RO water and tap water that is more similar to the tank parameters to avoid water change deaths?

I know the low KH in the tank isn't great since KH is important for buffering pH, but I don't know how to fix this without killing all my shrimp. I'm guessing the driftwood + substrate combo is keeping the pH down which keeps the KH down but don't know how to fix it? I welcome any thoughts, opinions, or even corrections to my logic haha! Thank you

 

[Aiken Drum]

I would get some second opinions on your water parameters. Try a different test kit, or get your fish store to test some samples. You should be able to get the parameters of your tap water from your water company, which will be far more accurate than any home test kit.

In terms of GH your tapwater is 2 to 3 degrees (sorry, I think in degrees) and your tank water is about 1.5 degrees. Both would be considered soft, so there isn't much going on there. So driftwood would explain such a small drop.

Your KH out of the tap is quite high, but in your aquarium its quite low. A bit of driftwood doesn't explain this large a drop, but only doing 10% water changes does. KH gets used up by a lot of the natural processes going on in aquariums, so over time it gets depleted. Normally KH is replenished by water changes. But it appears your aquarium is using up KH quicker than a small 10% water change can replenish it. A 10% water change is hardly worth doing, and will lead you to where you are, with tap water significantly higher KH than tank water.

A 10% water change isn't going to change water parameters enough to kill fish and inverts. If it is, it's being caused by something else in your water. If your aquarium water is 20ppm KH, and your tap water is 200ppm KH, after a 10% water change it should be 40ppm. Thats only 1 degree of difference.

What are you trying to do?

Get the tank closer to the tapwater? You need to do bigger, more frequent water changes than 10% weekly. I would start by changing 10% daily for a week. Then 20% every 2 or 3 days, Then get into a weekly 50% routine.

Get source water closer to your tank water? Yes, you need to use RO.

Your tapwater being high KH and low GH is ringing some alarm bells, as they would normally be similar. Is your tap water going through a water softener, either in your home or at your water company?

 

[freshwater_hedgehog]

This was super helpful. I was worried because I noticed a jump in molts the night of water changes so I was worried I was triggering pre mature molts causing deaths. But maybe the deaths are occurring due to water being too soft.

The goal is definitely to get the tank water closer to tap water since the KH in the tank is super low which i know is not great for inverts. But I want to do it in a way that doesn't harm the shrimp (which to your point it shouldn't since the total difference is super small). I was originally worried the 10% weekly was too much and causing large KH swings so that's why I was questioning using a tap water/RO water mix to raise the KH a bit more gently but sounds like that is probably not necessary.

I'll take your advice and hope for the best!

Yeah pretty sure my test strips are off. I agree the numbers seem suspicious. I'll look into getting more accurate measures. I live in a bigger city so not sure what water softening process they use but we don't use any extra measures other than basic aquarium water conditioner on my end.

 

[Aiken Drum]

The issue with water softeners is how they work. They use a principle called ion exchange.

Generally hardness in water supplies is caused by calcium carbonate disolved in the water. The calcium bit causes GH and the carbonate bit causes KH, so if one is high the other would normally be as well.

Water softeners run the water through a resin that strips out calcium and magnesium ions (which causes GH) and replaces them with sodium ions. So your GH drops, your KH doesn't, which is what you have coming out of your tap. Your total disolved solids (TDS) stays the same with calcium and magnesium replaced with sodium. Sodium isn't great in freshwater aquariums. Some fish are more tolerant than others though, and different water supplies go through more softening than others, so some people get away with it while others don't.

I've honestly no idea how freshwater inverts react to sodium.

This is what I'm concerned about really. I'm not going to dispute that your inverts are dying after water changes if that's what you are observing. But a 10% water change isn't going to cause a big enough fluctuation to parameters to cause that. So it's something else in the water. Sodium? Or it could just be your water changes are prompting a molt, and the KH is too low for the molt to be successful. While I do keep shrimp and snails, it's not really my area.

 

[Autumnsky]

Does your city use chloramines? It's stronger than Chlorine. Some water conditioner brands don't break them down, or it needs a double dose. You can check the water provider website or probably call them. I'd also ask if they use other chemicals which could harm aquarium inhabitants.

I know in my area, the city was doing a lot of pipe replacements and additions for a growing area. They would flush the system with other very strong chemicals to kill off contamination from that being opened up.

And also look to make sure your conditioner treats heavy metals, like iron or if you have lead or copper in the pipes in the city/ or your home.