Out of control Ph

[Mrfixit246]

Warning: very long post.

1st I'll give you the complete history on this tank.
75 gallon tank I bought 6 years ago. Previous owner tried to keep African Cichlids but kept killing them. After a couple hundred dollars in fish he gave up.

The tank has older 350 magnum canister filter with ceramic and carbon media also a HOB biowheel penguin 300 with filter and charcoal. Gravel bottom with under gravel filtration with 4 bubblers.

I got the tank 5 years ago when My goldfish were getting too big for the tank and cleaning the tank became a 2-3X a week chore. 3 large goldfish did well in there for 3+ years had a Ph spike and lost 2. The last Comet GF got to be about 8" and also too big for the tank and sent him out to the farm koi pond. That was about 18 months ago. I kept the filters and bubblers going in the tank after doing a good 50% water change and gravel cleaning. and twice in the 18 mot=nths I cleaned the gravel and did a 50% water change.

Fast forward to about 3 weeks ago I wanted to get the water ready for tropical fish. Checked the chemistry and here is what it read:
pH 8.6
ammonia 0
nitrites-0
nitrates-10ppm
Did a 50% water change used Seachem Prime to treat the water, double dose. Water here is real hard and treated heavy with chloramines.
waited 24 hours and rechecked water only changes
Ph 8.4
ammonia slightly above .25ppm

Now I decided to checked my water at tap Ph 7.8 ammonia(chloramines) 10ppm My ph wasn't coming down on its own.

So I do a complete tank drain and cleanout below the gravel filters and everything. kept the biowheels in tank water. double dosed with prime again. and waited 4 days. ammonia was at .25ppm and ph jumped back up to 8.2. Now I still don't know WTH is going on with this tank.

I tried a whole bottle of API Ph down and barely moved the Ph and only temporary.down to 7.8 next day back up to 8.2

I read up on lowering Ph and with no fish yet. I could do drastic measures. so I used vinegar to try to drop it and after triple dosing over 5 days ph would only temporarily drop to 7.8 then it came back up. Now I'm pissed I drop in a 4X dose on vinegar and Ph dropped to 7.4 next morning a complete fog bank in the tank. I suspect carbon dioxide from the reactions of the vinegar. Waited 3 days and started to clear and checked water and
Ph 8.0
ammonia .25
nitrites 0
nitrates 10ppm

Something in tank is buffering the Ph. Now I am getting crazy about getting this Ph in check. I buy a reversed Osmosis system for our drinking water (I didn't tell the wife also for the tank). I spend 3 days storing 30 gallons of water for a change out and yesterday morning I did a 30 gallon water change. Water chemistry now:
Ph 8.0
ammonia 0
nitrite 0
nitrate 0

Also I forgot to mention previous owner had the Charcoal media filter blowinto the tank so in the gravel is mixed with some charcoal. Could that be buffering my Ph so anything I do I would have to do triple to make anything stick?
Do I keep doing water changes until it drops? Do I drain the whole tank and replace the gravel?
I'd love help. I really want fish in this tank but DO NOT want to kill anything if I can help it.

 

[Delapool]

Do you have kh / gh (and other) readings for tap water at all? It sounds like kh is high so every water change will reset ph.


Carbon won’t impact ph but carbonate in gravel will eg crushed limestone or shells.

 

[Mrfixit246]

Thanks for the reply.

I don't have test kit to read kh or gh, but I can tell you my tap water is very hard. The city water tests say the hardness is 38 grains.

I think you are onto the problem. for 18 months I added water when the level got low. the TDS is probably very high in the gravel. I am going to try a couple more 30 gallons water changes and I'll get a kh test kit. I'm using RO water now for the tank.

Thanks

 

[Mrfixit246]

Update

I bought a Kh Gh test kit. My water in the tank before the water change out. was
Kh=214ppm
Gh=off the chart 14 drops
Ph=8.0

Did a 50% water change with RO water
Now the chemistry is:
Kh=125
Gh=175
Ph=7.6

Looks like Ph was being affected by the TDS from a couple years of putting in water without removing enough of the TDS. The gold fish I had in there initially didn't mind the higher Ph.

Thank You Delapool for your advice. Looks like you were right on!

 

[Mrfixit246]

Tank update

Here is an update on my tank Ph issues.

After a little over a month my Ph is now 7.2. I have done about 4 water changes using RO water. with 10-15 gal each time in a 75 gal tank.

The first couple water changes the Ph would drop from 7.8 to 7.4 then a couple days later would bounce up to 7.6 then creep up to 7.8 again. Something was buffering. only after the 3rd water change did the Ph stay lower only creeped up to about 7.6 then after the 4th water change the water stayed at 7.4 after 3 days.

The suspected problem was the TDS(total dissolved solids)was off the charts(over 212) to start with and now is about 71ppm. I'm thinking that was what was buffering the Ph. All the other numbers have held steady and I now have fish living in the tank for 2 weeks.

Thank You for all the help!

'Fixit

 

[Caliban07]

Here is an update on my tank Ph issues.



After a little over a month my Ph is now 7.2. I have done about 4 water changes using RO water. with 10-15 gal each time in a 75 gal tank.



The first couple water changes the Ph would drop from 7.8 to 7.4 then a couple days later would bounce up to 7.6 then creep up to 7.8 again. Something was buffering. only after the 3rd water change did the Ph stay lower only creeped up to about 7.6 then after the 4th water change the water stayed at 7.4 after 3 days.



The suspected problem was the TDS(total dissolved solids)was off the charts(over 212) to start with and now is about 71ppm. I'm thinking that was what was buffering the Ph. All the other numbers have held steady and I now have fish living in the tank for 2 weeks.



Thank You for all the help!



'Fixit

I wouldn’t class 212 as off the charts. One of the places I used to get fish from (subsequently died not long after purchase) were sending fish in water with a TDS of over 800ppm.

Glad you managed to sort your pH out though.