Moving to Low Hardness -- How Should I Manage?

I do about 40% twice weekly on my 10 (I try to do about 50%, but right now it's on the floor and the syphon runs out). Just for kicks I took some measurements before and after. Off the top of my head I think that it went KH: 100 - 70 and pH stayed const. at 7.2. This was right after adding, though, I wasn't thinking about CO2 equilibrium at the time.:rolleyes: , this may have changed things a bit, but since the pH seems pretty const. from week to week, I doubt it.

This is only my humble experience, mind you. You may well have very different results. Although I'm setting up a 33g planted shortly, so hopefully I can pull off the same results.
 
Originally posted by TPIRman
Hi all --

The tank is a 30G, and it'll be filtered by an Eheim 2213 with a FilterMax III pre-filter. I use two tablespoons of crushed coral on my 10G now, so I was thinking of starting with six tablespoons and going from there.

Also, to double-check, you all think I'll be fine with 40% changes straight from the tap?

Thanks again,
John
Click to expand...

40% changes shouldn't cause excessive swings in either pH or KH. You may see a bit of a change, but nothing harmful. Obviously, testing before and after a change is the best insurance, but even without that you should be fine.

Let us know how it turns out!

Jim
 
Update

Here's an update and a thank-you to those who helped me out. The 30-gallon tank is now set up. To raise the KH, I put 6 tbsp. of crushed coral in a filter bag, and put this in my Eheim 2213. I decided to go whole-hog and attempt 50% water changes with the Python to see if the KH would remain at an acceptable level. Here's some data:

Tap pH/KH (after sitting out 24 hrs.): 6.6/24 ppm

Tank pH/KH before WC: 7.0/72 ppm

Tank KH shortly after 50% WC: 52 ppm

Almost what you would expect mathematically. The fish have shown no ill effects from this temporary dip in KH, and within a couple days the alkalinity returns to its normal level in the low- to mid-70s.

I'm not adding CO2 yet, so the water chemists among you might have noticed that the pH and KH values don't seem to match up. I supposedly have a CO2 level of 10 ppm in my aged tap water, and about 12 ppm in the tank water.

I'm trying to figure out what is causing these readings. I'm not adding anything to the water except dechlorinator (mostly for the chelating agents), and phosphate tests show very low levels. If anybody has insight into this strangeness, I'd appreciate it, since I'll be adding DIY CO2 this week and would like more reliable readings.

Thanks again to all who helped me prior to the tank setup. It allowed me to approach this issue with confidence.
 
The KH-pH-CO2 relationship assumes that all your alkalinity (KH) is from carbonate species. If there are any other buffers in your water, this will affect the theoretical CO2 concentration.

The most likely culprit is PO4 every 1 equivalent of PO4 has a 3-fold effect on KH, but since you say it's testing low, it must be something else. I couldn't say off the top of my head.
 
When we moved from our old house (artificially softened water with a moderate concentration of hydrogen sulphide [H2SO4]) to our current house (hard, chlorinated water treated with AquaSafe) we lost two ram cichlids and some tetras due to dissimilar water conditions.

You can also use limestone to harden water. It is far easier to get than coral sand.
 
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