u/2legit2quit6969

Hi all,

Following up on a previous post I made.

Current State:
• Tank Size: 5 Gallon
• pH: < 6.0 (API test is bright yellow, likely lower)
• Ammonia: Present (Ammonium due to low pH)
• Nitrite/Nitrate: 0/0
• Substrate: 50% old substrate (from a prior cycled tank) on bottom, 50% new sand on top.
• Inhabitants: Just lost an Amano. 1 survivor remains.

The Backstory:
I had to emergency swap a cycled tank due to cracked glass. I moved everything: the filter media, all the plants, the water, and half the old substrate (layered under new sand). Since the move a month ago, the cycle has completely stalled. It’s an acidic, ammonia-driven environment that won't budge.

The Current Struggle:
I’m using purified water and just started using a NeoTiger GH/KH+ remineralizer.

• The Sink: When I add remineralized water to the tank, it does absolutely nothing. The tank "eats" the KH and the pH stays at rock-bottom yellow.

• The Seiryu Factor: I recently removed a Seiryu stone because it was spiking my GH, but now I realize it was likely the only thing keeping my pH from crashing. Since removing it, everything has gone south.

• Plant Melt: My plants are rotting specifically from the bottom up. The bottom halves turn to mush/erode, and I’m constantly pulling them out to clean the rot.

The Plan/Questions:
I have Fritz Turbo Start on standby, but I’m waiting for the pH to hit at least 6.5 so the bacteria don't just go dormant.

1. Is the buried old substrate creating an "acid trap" or an anaerobic mess that’s killing my plants and eating my buffer?
2. How do I raise the pH safely without the Seiryu stone, given the "acid sink" effect?
3. Should I just pull the remaining shrimp and do a 100% substrate reset at this point?

TL;DR: Swapped tanks a month ago, layered old substrate under new sand. pH crashed below 6.0 after removing Seiryu stone. Now in a permanent "acid sink" where KH is eaten instantly, plants are rotting from the roots up, and the cycle won't start. Please help!

Thank you!

Looking for help with a 5-gallon tank that I think has been repeatedly crashing after a tank swap / substrate change.

A couple months ago I set up a 5-gallon planted tank. Then a little over a month ago, that tank cracked, so I had to move everything into a new 5-gallon.

When I moved it over, I kept:

\- all the old water

\- the old filter media

\- some of the old substrate

But I did not keep all of the old substrate. What I did was put the old substrate on the bottom, then added a significant amount of new substrate on top. More than half of the total substrate in the current tank is new.

At the time, I assumed keeping the old water, old filter media, and some of the old substrate would preserve the cycle well enough. For a while I thought it had. But looking back, I think the tank never really stabilized after the move.

Over time I started getting repeated ammonia spikes. Sometimes the ammonia would temporarily come down, which made me think the tank was recovering, so I added more shrimp. In hindsight, I think I added livestock into a tank that was not actually stable, and that made things worse.

So now I’m trying to figure out whether this is basically:

1. a substrate / cycle crash from the tank move,
2. an ongoing re-cycle because too much of the substrate was replaced,
3. or something else I’m missing.

Symptoms / pattern:

\- repeated ammonia spikes, including up to around 1–2 ppm at the worst

\- nitrite has often read 0, which has confused me

\- nitrate has sometimes been very low or 0 as well but frequently up to 30/40

\- tank got cloudy multiple times

\- tank had a bad smell for a while

\- livestock started dying off over time

\- I kept trying to correct with water changes, but ammonia kept rebounding

At one point I thought decaying plant matter / mulm might be the problem, and I did remove a lot of that. I also reduced livestock. But even after that, the ammonia kept coming back.

Stocking had been:

\- mostly Caridina shrimp

\- some Neocaridina

\- a few dwarf crayfish

At this point almost everything is dead. I think I have maybe one dwarf crayfish left and possibly one shrimp, plus plants.

Current setup:

\- 5-gallon planted tank

\- regular filter with sponge over intake

\- bubbler / air stone

\- heater was used but is currently off (tank is high 70s)

\- old filter media is still in place

My main questions:

\- Does this sound like the tank is basically re-cycling because of the substrate change?

\- If so, should I basically stop messing with it other than water changes and let it stabilize for 1–2 weeks?

\- How often should I be doing water changes if ammonia keeps showing up?

Any help appreciated. This tank was running great but once I needed to rehome them due to the crack, I haven’t been able to get the tank stable :(

Please help my poor shrimpies!

TLDR; I changed tanks after a crack, reused some old biological material but replaced a lot of substrate, and ever since then my 5-gallon shrimp tank has been repeatedly crashing with ammonia. Did the substrate change cause a re-cycle, and what should I do now?