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Please help why my water KH drops in one week to from 18 to 2

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professorjimjam

Dovii
MFK Member
I have had a fish tank since 2020, when COVID started. I have gained experience with many different kinds of fish, but no matter how experienced I think I am, I still encounter new challenges that make me feel like a beginner.

Currently, I have Malaysian Trumpet Snails (MTS), Bristlenose Plecos, and guppies in my tank. The tank is not overcrowded. In fact, compared to what I had before, it is moderately populated. It is a 32.5-gallon tank with three plecos, five guppies, and a mix of MTS snails and a couple of ramshorn snails.

When I first started, I always changed the water every two weeks, particularly when I had a heavily populated tank with puffer fish. However, once the population decreased to just guppies and a few plecos, I reduced the water change frequency to once every 30 days, changing 50% of the water. This routine worked until I began to notice significant algae buildup on the walls of the tank. I cleaned the algae every time I changed the water.

Recently, I noticed erosion in the apex of my MTS snails’ shells. After seeking advice from the community, it was suggested that I test the water parameters. Upon testing, I discovered that the pH and KH levels had dropped significantly. In response, I performed an 80% water change over two days to avoid shocking the fish. After the water change, the pH improved to 8, and the KH rose to 18. This happened on January 20, about a week ago.

However, today, I tested the water again and, to my surprise, found that the pH had dropped to 6.5, and the KH had decreased to 2. I am not sure what is causing this drastic drop. Could it be the fish? The plants? The plecos? I need help understanding what exactly is causing the KH to fall from 18 to 2 in just a week.

I read online that adding baking soda can help increase KH levels, but I am unsure if this method is safe for my fish. If it is safe, how much should I add (in teaspoons), and will it harm the fish? Other water parameters, such as ammonia, nitrate, and nitrite, are all within acceptable ranges, but the KH remains an issue.

I do not want to perform an 80% water change every week. The tap water I use has a pH of 8.5 and a KH of 20, so it is quite hard water. However, when the water remains in the tank, the pH and KH drop significantly.

If the snails are causing the issue, why did they not cause it before?

I am exhausted and need help resolving this problem. Please help me figure out what is causing this and how to fix the water without changing it every week.

Thank you.
 
Suggestion:
Fill a clean container with tap water. Allow to sit idle 24 hours. Then test PH/KH. Are they consistent with tap water from the day before, or closer to your tank water after a week of hosting fish?

Charlotte, NC (where I live) has quite soft water. This was true for me in several homes and is/was commonly discussed in our Local Fish Club. But in 2006 I moved to a new house and suddenly the tap water tested with a PH of 8+. Being quite different I was very concerned. Long story short, with most of the details escaping memory, I learned that after 24 hours the water settled out and all readings reflected soft water the same as everywhere else in the city. I continued to use my water without any doing anything different. My fish showed no ill results and I was breeding a wide array of SA/CA Cichlids at the time.

From what I remember, it was concluded that somewhere along the line something was getting in my water that created artificially high readings that gassed off after a day or less.

I saw your other thread and read most of the posts there. Ramshorn snails in my water also have very fragile shells. I consider snails pests, not pets, so it's never been a concern of mine. I haven't dealt with MTS in a long time so I can't comment there. But since I said that out loud I'll probably have them next week.
 
Toby_H said:
Suggestion:
Fill a clean container with tap water. Allow to sit idle 24 hours. Then test PH/KH. Are they consistent with tap water from the day before, or closer to your tank water after a week of hosting fish?

Charlotte, NC (where I live) has quite soft water. This was true for me in several homes and is/was commonly discussed in our Local Fish Club. But in 2006 I moved to a new house and suddenly the tap water tested with a PH of 8+. Being quite different I was very concerned. Long story short, with most of the details escaping memory, I learned that after 24 hours the water settled out and all readings reflected soft water the same as everywhere else in the city. I continued to use my water without any doing anything different. My fish showed no ill results and I was breeding a wide array of SA/CA Cichlids at the time.

From what I remember, it was concluded that somewhere along the line something was getting in my water that created artificially high readings that gassed off after a day or less.

I saw your other thread and read most of the posts there. Ramshorn snails in my water also have very fragile shells. I consider snails pests, not pets, so it's never been a concern of mine. I haven't dealt with MTS in a long time so I can't comment there. But since I said that out loud I'll probably have them next week.
Click to expand...
thank you so much. I will for sure do the test of the water to allow it to sit idle 24 hours and then test the KH and PH.
 
Let us say that I test my tap water after 24 hours and find it to be soft, with a KH of 2 or even 1. What should I do in this situation? If it is only going to affect my Malaysian Trumpet Snails, I am not concerned. However, if it could impact my other fish, how can I adjust the KH and pH of my water appropriately?
 
Personally, I live in an area where my tap water is very close to the water of most of the fish I keep.

I've often heard that stable water parameters are more important than specific water parameters. Meaning, if my fish are native to an environment where the PH is 6.5. And my local tap water is 7.5. Its better to keep them at 7.5 consistently, than to use buffers which will usually result in the PH varying between 6.5~7.5.

That said, Duane recently posted, and Kevin at TUIC reinforced, how fish native to soft water evolve resistance to things that occur in soft water but do not evolve resistance to things that occur in hard water.

So, there are pros and cons to either approach. I personally choose to stick with my local water parameters and not buffer.

As for your fish... Most tank strains of guppies are so far removed from "native environments" I don't think it really matters. And they'll flourish in almost any relatively clean water. Bristlenose Plecos also do fine in softer water. I've bred them in my local water a number of times, as have multiple people in my Local Fish Club.

I personally would not buffer unless proven absolutely necessary. And in that case, I'd plan the process to avoid constant swings in the parameters. Which usually means incorporating some form of a holding tank to store & condition water prior to adding it to your tank.

Adding Crushed Coral to your tank is one of the easiest ways to buffer your water. But when doing so the PH drops at every water change (as your adding soft water), then creeps up over the course of the week, only to crash again the next week. Adding baking soda is a safe way to buffer, but again, if you do a water change the PH will drop. Then you add the buffer and it pops back up. Then as your water settles it will likely fluctuate a small amount. And each time you do this you it may not be exact. And in this way your fish are constantly dealing with fluctuating parameters.
 
Baking soda will buffer alkalinity for a short time, but only temporarily
Even though you have fewer fish, the ones you have still produce nitrate, and with few water changes, with the less buffering capacity you had, a stable alkalinity was depleted long ago (especially with soft water). hence the algae, the drop in pH, and consequently, the snail deaths, compromising their shells making them weak. Somethin we didn't know, regarding your previous snail death post.
Unless you get back to doing enough water changes to keep alkalinity stable, the decline will continue.
A 50% water change only every 30 days is not going to cut it,
To me a 40% water change once per week "might work", to get a handle on the nitrate load.
I would do a nitrate test after soon after a water change to see if it is making a dent.
Your goal should be 5 ppm nitrate consentration (or less) especially knowing now, about your soft water.
 
Last edited:
I buffer / stabilize my livebearer tank with crushed coral....since my tap water is soft with low GH and KH. I prefer the word stabilize, as it helps to "maintain" KH, and prevent a PH drop.

With that said, I change water weekly, and sometimes even more frequently. I make the water changes quick and easy: siphon into a nearby drain, and refill with a python. I also use a bit of baking soda on the water change to help match the higher PH of the tank. (It's not rocket science....just measure what a given amount of baking soda will do to a given amount of YOUR source water.)

The easier you can make the water changes, the less chance of putting them off.
 
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