Low pH. Is Purigen the culprit?

My 30gal tall has been cycled for five years, and has run at a consistent 7.0. Driftwood and Indian almond leaves have kept it the color and clarity of low-quality, weak tea. I recently decided I wanted to see the colors of the inhabitants better (because they're extra pretty!) After researching for safety, I decided to try Purigen about five weeks ago. Crystal clear, with no particulates after about 36 hours. Impressive! Downside: all that clarity = algae that's mostly clinging to that fake plant clump at top middle (I am going to take it out and clean it.) So, I decided to get a couple of nerites (have had them before - at one point in all seven of the tanks I had.) They croaked after two days (upon returning them is when my LFS alerted me to my low pH.) Dosed with Seachem's neutral regulator. Decided to get some mystery snails a week later. They're pretty, and I previously had one that lived for over a year. Not this go round: I just disposed of one of the four mystery snails this morning after QT'ing it for a few days to be sure it wasn't playing possum. I'm worried about the remaining three. One in particular ain't lookin' so hot (I'm watching it like a hawk bc of course I don't want a hidden dead snail mucking up the whole habitat.)

Since all this started, I test my pH weekly (including today,) and it keeps coming up low (I'm using two tests now to confirm.) So I add another dose of the neutral regulator. Adding the Purigen is the only thing that's changed this whole time (I did add a small cuttlebone (bottom right of pic) for the snails, but the pH drop had begun just prior to adding it.)

I have three questions:
1.) Is it the Purigen, even though it's not supposed to cause a change in pH?
2.) My fish are fine, and I know they can adapt more readily than snails; however, attempting to repeatedly alter the pH using chemicals is beginning to worry me as I'd hate to lose any of them. Does this mean if I use Purigen, I can't have snails?
3.) Is there something else I could use that results in the same water clarity? Would removing the Purigen from my HOB and replacing it with Poly-fil get me close?
4.) Okay, four questions: I could never find info on whether or not using Purigen to remove the *color* of tannins also removes the *benefits* of the tannins. Does anyone have a definitive answer?

Specs:
Inhabitants: Betta sorority of nine pretty ladies. Corydora that breed like rabbits, so I must be doing something right. After giving about a dozen to a friend a while back, it's held steady at 9-10 (cory eggs are snackable for at least one of the more recent occupants, which is fine by me.) Seven neon tetras. Three mystery snails.
1.) 30 gal tall
2.) cycled 5 years; 25-30% WC every three weeks, rarely any mulm because the corys. WCs/in-between water topoffs w/ Prime (come to think of it, using Prime vs tetra or api water conditioner *is* something recent. But certainly it's not the culprit...)
3.) Aquaclear 30 (I think) HOB, with bottom to top: coarse sponge, fine sponge, ceramic media, purigen
4.) Double sponge filter with ceramic media in the hoppers. I also keep a bag of extra media hanging beneath the output of the HOB for quick setup of QT/hospital, etc.
5.) heater/LED lighting
6.) black sand substrate & same rocks since day 1 (fake plants)
7.) driftwood that's been in there four years after mega scrub and lengthy soaking.
8.) Indian almond leaf because it's good for bettas. I keep one in there until it begins to tear apart, then I replace it.
9.) Parameters:

• pH - 6.0 (I've begun using pool/spa strips as an "easier" step one, then using API master test to confirm)
• Nitrite 0
• Total Ammonia 0 (brand new API drops)
• Free ammonia 0 (Seachem constant monitor seen at left of tank in enlarged pic. Edit: it got cropped)
• Nitrate ??? See pic. Historically, between 20-40. The drops from bottle #1 came out this same orange, which seems suspect. I'm beginning to think this kit has gone bad before its actual "use by," hence the separate pH strips, the new Ammonia test drops, and the constant free ammonia monitor. (According to the drops in my master test kit, everything in this tank should be dead, including the fake plants.)
• Per pool/spa strip, not sure if relevant: total hardness 250ppm; alkalinity 40ppm; pH "very low," as in below the strip's register.
• Also per pool/spa strip (also maybe not relevant) Our tap water tests at 7.0pH; hardness is neither low nor high; alkalinity is 120ppm (water source is the Memphis Sands aquifer.)

Included a pic of the whole thing, in case there's something that stands out as problematic. Sorry about the glare, and blinds and such. I tried. Also note, those are white peacock feathers on black cardboard behind my tank, not some crazy mycellium

 

With a tank running 5 years and a schedule of 25% WC every three weeks, you may be experiencing OTS. One of the results of OTS is the ability of the tank to hold/buffer the PH as the minerals that help it are not replenished fast enough. Purigen might have just brought it to light quicker whatever the issue is.

Since your tap is at 7 with the low kh, I would try doing partial water changes daily to see if that might bring back some balance. Maybe 10-15% everyday for the next week (until 100% has been changed) and see how it fairs. The snails dying in there probably also contributed to the increased acidity.

And yes...test kits do expire. Several years after the lot date, and they can no longer be reliable.

PolyFil can help polish the water but it's dependent on the flow of the mechanical filtration on how much movement there is.

 

Your KH is low. Below 7 pH youll be relying on organic buffers to keep pH stable. That means leaves and tannins which Purigen may remove

 

I am sure cherryshrimp is correct. Purigen definitely removes tannins. The buffering effect of the leaves you added was removed and pH dropped. And yes, I believe that purigen does remove the beneficial properties of the leaves, best to use another method of improving clarity. If you want a lighter stain you can adjust with water changes, and using fewer leaves.

The fish you have will be quite happy at pH6, but snails probably won’t.

 

Thanks y'all. I'll try the WC suggestion above, and also subbing polyfil for the Purigen. I really do love seeing the colors of my fish, but I might love more the idea of them receiving the health benefits of tannins. For the time being, I think I'll move the snails to a separate habitat.

Ordering a new kit today. Hopefully it's not OTS I'm dealing with.

 

It is likely a form of OTS in a sense... Rains generally dilute and bring in new nutrients to a lake or river, in an aqaurium the water change kind of has to do that. If you tank is 100% of the water volume and you do a 25 or 30% change per month, you leave behind 70-75% of the water month after month to slowly degrade the KH to zero and then the pH drops with it. With the tannins and humic substances (organic compounds from long term organic decay) they will act as a buffer and head your tank toward low pH "blackwater" which is fine for species that like it.

Water changing more basically solves the issue of the KH fallout and pH drop.
Not removing the humic substances with purigen or carbon or other methods will keep it as "black water" and low pH and safe for species that like that type of water and not have to water change so much, but still remain consistent and basically just doing it to lighten the water color over time to a coloration you can live with.

If you want your tank to be like your tap water, you really need to aim at changing water so that 100% of the tank volume has been refreshed every 30 days, this will get rid of the water staining though and may not be what you want but it will get tank in line with tap if you want rid of the blackwater biome.

Running blackwater, low pH is a fact of life. Snails and shrimp are a no go, the acids in this environment will attack their shells and they won't live long, and that's the thing, the acids are what drops your pHand your KH, it's what keeps many of the bacteria at bay, and what keeps the water really clear, the tannins and humic substances is what keeps it stable and safe, but you have to limit yourself to species that thrive in blackwater/low pH environments for longevity of life. Then try to maintain the water color where you like it though small water changes and adding new leaves and things to maintain the color and stability.

Ideally you'd want new water to have GH and KH from 2-5 degrees, (35ppm - 90ppm) low in mineralization, for water changing. it takes a long time to get from your tap water parameters to your tank parameters any drastic water changing with your tap water at this point will likely destroy the blackwater tank you've built over the years, so really think hard before deciding to go that route.

The tanks 250ppm hardness (14dGH) is problematic as its out of range even for your tap water which means calcium and magnesium) this is a sign there isn't enough water change and as the KH gets burned off from the calcium carbonate, the calcium is going to the GH column and building up, the carbon is also building up in there in an increasing TDS.

So yeah you have "blackwater tank" technically, but its far from ideal conditions for let's say, neon spawning,

Perhaps a 20-25% water change each week, will gain ground on it and get you blackwater while maintaining the low KH and pH, while getting your GH down to your tap water level... perhaps peat in a bag in the filter will trap the excess GH minerals and lower it down to the ideal range.. honestly for blackwater, distilled, ro or rain water is the best to not increase GH any higher and get it lower than tap water is then it's just finding the right ratio mix of tap and filtered or rain water to keep things where you want them.

Not sure what you want to do if you want to continue the blackwater tank path, or you want to recover it to your tap water parameters.
But the high GH (higher than your tap water) is a clear indication that water isn't being changed enough and OTS is either there, or on the horizon shortly.

 

Thank you for the detailed info!