50 Gallon Tank Low pH and kH, high GH - advice sought

  • #1
Hi everyone,

I have a 200L freshwater tropical tank with some unhappy fish. The tank has neon tetras, a few gouramis, two tiger loaches, a pleco, and some mollies. I'm still a newbie so learning about water chemistry.

I think they're unhappy because of pH issues. My tank reads from the test strip!

GH: 180 (highest value on strip)
KH: 0 (lowest value on strip)
pH: 6

I need to raise my KH and pH, but don't think i should be raising the GH since it's already so high. I've read that using the crushed coral, which is good for KH and pH, will also raise the GH.

Very appreciative of any advice here. I use dechlorinated tap water currently.
Sorry, should have added that both nitrates and nitrates are 0. The tank has gravel bottom.
Sorry, should have added that both nitrates and nitrates are 0. The tank has gravel bottom.
  • #2
Firstly when you have finished the strips get some liquid reagents. They are much more accurate.

There are several ways to fix the ph. It really depends on how you want to go. First thing to do is to figure out where the high gh is coming from.You should test your tap water. Then look at things that that leach calcium and magnesium This is why coral, calcite and chalk will raise both kh and gh. They are mainly calcium carbonate. The carbonate adds to kh and the calcium to the gh.

To raise ph, raise kh. You can as you say add coral. My experience is that it will raise your ph by about 0.6. You can buy a commercial buffer such as seachem 7.0. You can use something like sodium bicarb one tsp per 5 galls to raise by ph of 1. You should be aware that if kh is 0 then you have no buffering capacity. That means that ph will be very unstable and it will stress your fish. The last two will add buffering capacity. The coral will tend to neutralise acids and so act similarly bringing stability to ph.

You need to change these parameters slowly- ie slowly dose with the bicarb or buffer over days - because swift changes affect fish more than parameters out of whack.

You really need to know what parameters you are aiming at. I create a spreadsheet with each fish and their parameters. I then figure out where the overlap is and that is what I aim for.
  • #3
Is it possible your fish are unhappy because of something other than the ph and hardness? Neons typically enjoy soft acidic water. Is your tank fully cycled? I would check your ammonia. “A few gouramis” might be unhappy together because they can be territorial unless they have enough plants to demarcate territories. Most fish store fish are pretty adaptable to different ph and hardness values. Nonetheless, mollies prefer hard water, and neons like soft water.
  • #4
My tank had this problem. I added crushed oyster shells and that took care of it. Without the crushed oyster shells, the pH was crashing overnight and there was no stability for the fish.

My GH is 9, KH 4, pH 7.5. Everything became stable after adding the calcium.

I'm no expert, but it seems like maybe you will need different tank water. RO or Distilled, then add back the necessary minerals. You definitely need something to buffer the water and coral or oyster shells seem like a great option.

I added 1/4 pound of oyster shells per gallon.
  • #5
You can use something like sodium bicarb one tsp per 5 galls to raise by ph of 1.

PH is on a logarithmic scale. The amount it takes to raise from 6 to 7 is 10 time more than the amount yo raise it from 5 to 6 and 1/10 the amount you need to raise it from 7 to 8.
  • #6
what does your source water test at, pH GH, KH compared to the tank?

What is your nitrate levels? How long has the tank been running?

Don't change anything at all right now, your pH being at 6 is protecting your fish from ammonia. if your source water comes like that it is handled one way, but if your tank has gained GH and Nitrates and lost KH and pH over time, it's corrected differently. because if you bring up the pH, the ammonia will become toxic, and if this is a new tank then it's not cycled and handled differently also.

Have to be sure of the cause and age of the tank before deciding how to correct it. because handled wrong the fish will die and doing nothing at all would be a better solution, they might not be happy, but they aren't hurting and dying either.

really the only way nitrates could be 0 is if it's new water and no cycle has been done yet so no ammonia conversion to nitrates. if this is the case, raising the pH is the LAST thing you want to do without getting on top of the ammonia which is pH bound into ammonium first.

My opinion, if this is a new tank set up, take the fish back to the store and surrender them. your water quality issue is too advanced for your skill level to try to fish in cycle the tank and raise pH and KH and it's much easier to do and learn what to do, without worrying about killing your fish to find the balance that you need to have.

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