Question about Water Chemistry / Tank Setup

[DaveT]

Hiya

I keep three bare fish tanks, I use an RO filter then rebuild my water back up to pH 7.8 gH 4 kH 4 TDS is approx 200-220.

Now my two breeding tanks are pretty stable, i use the kH /pH measurements to mearsure when to do a water change (takes about a week for the pH to drop down to 6 at which point i do a waterchange(pH back up to 6.6 ish).

My main community tank on the other hand the pH drops like a rocket and i must do water changes every third day just to keep the pH from dropping below 6. Now i fully understand that this is down to the higher bio load and a lack of buffer, and am getting a little worried that my tank pH is swinging to much (w/c trigger level is ph6, after a water change the pH is back up approx 6.5, i know its only 0.5 swing but that climb in pH takes place in the space of one evening and surely cant be good for my fish.

so im looking for advice on how to stabilise the pH a little.

At the moment ive thought about rebuilding the RO water with higher pH/kH, this can be an easy fix but surely this will still leave me with large changes in pH when i do the w/c (unless i do them daily,which i wouldnt mind most of the time but i dont want to be worrying should i have to miss aday for whatever reason).

The other thought ive had is to add some coral sand to the tank (and possibly the other two tanks), the stuff ive seen is 3mm coral sand (looks like normal beech sand, not the white stuff like marine tanks use). the problem i have here is that if i add 1/2 an inch of this stuff to my tank will it buffer it too much? the main occupants in this tank are a couple of 4.5 inch Discus and a 2 - 3 inch Goldy plec (scobyancistrus Auratus).

Id quite like the sand idea but am unsure where that would leave the natural buffer levels of the water.

I dont mind altering the pH /kH of the rebuilt water to compensate but am unsure how much i would need to compensate. anyone thats done similar i would love to hear from you.

any one got any input / ideas or suggestiongs. all are greatly appriciated.

Thanks

DaveT

[MatsP]

I'm not quite sure what you are actually saying, because it sounds like you are filling the tank with pH 7.8 water (which seems awful high from a RO water), and then it drops to under 6 in a few days. That's a HUGE drop.

Sure, coral sand will help improve the pH-stability.

--
Mats

[Bas Pels]

If I read correctly, the rebuild RO water is pH 7,8 the tank is 6,0 and after waterchange with this water 6,6

Now I wonder, if 7,8 is OK, why would you use rebuild RO water in the first place? From the specs I get the idea the pH is rather high, but the water is soft - a water type rarely found in nature

tds (measured by conductivity) of 400 or even 500 would not be a problem, just as a KH of, say, 10.

This would buffer (that is, stabilize) the pH, just as adding coral sand

Should you, however, prefer more acidic water, this could be stabilized with peat and/or wood. Both lower the pH, but after a while they start buffering

[DaveT]

Hi Bas

Thanks for the reply, the high pH is due to using bicarb for rising the kH, hence i dont want to add too much more.

The water chemistry i was aiming for originally, was aimed at keeping discus, where the soft water was more critical than the pH, i tried the same water on my hypancsistrus and they started breeding so now i use the same water on all my tanks.

Im guessing then that im better off using coral sand or similar to buffer the water up as i dread to think what the pH of the rebuilt water would be if i was to use bicarb to take the kH up to 10.

If i add sand to the tanks then, i would add more bog wood, at the moment i restrict the use of it due to its effects on the water.

So my way forwards at the moment will be to add some coral sand to the tank and monitor the parameters, adding wood/peat if it starts to get too high, hopefully i can find a natural balance between 6 and 6.5, i suppose id be happy with, pH 5.5 to 6 aslong as it was more constant than at present, i realise i may not get that without rising the pH and kH of the tank.

I guess the main thing im trying to do is get a natural buffer in the tank so i dont have to rely on the waterchanges to add buffering capacity.

If im heading in the wrong direction on this please point out the flaws.

as it is now im going to buy some sand on payday and slowly start adding it while monitoring the water parameters.


Thanks for your input

Dave

[MatsP]

I have been using coral sand in an attempt to add buffer to my automatic water changing system. That DOESN'T work - but that's basically 2kg of coral sand which the water flows through before dropping into the sump filter, and whilst my initial attempt when trying it out worked really well - I got a TDS of 600 or so, I found that the TDS increase soon went down to about 15 PPM difference between "before" and "after". So now I add a "RO fixup" additive (which I suspect is mostly bicarbonate).

I also think that there is little difference between adding buffer through coral sand or simply adding (dissolved) bicarbonate to keep the pH stable. In the end, what you need in the water IS bicarbonate. Whether that comes from coral sand or powder in a tub.

--
Mats

[Mike_Noren]

The difference between adding a "balanced" alkalinity booster like limestone and just adding bicarbonate is that the alkalinity will slowly drop after adding just bicarbonate. This is because the water will strive towards equilibrium with the atmosphere by releasing CO2.
So if you start with water with alkalinity of 4 dKH & pH 7, then add bicarbonate up to 10 dKH and pH 8, and wait a couple of weeks, you'll be back to 4 dKH and pH 7. The only difference will be slightly higher conductivity due to sodium.

Limestone reacts with acid in the water to raise pH and release bicarbonate and calcium. The reaction is rapid at very low pH (if you drip acetic acid on limestone it reacts violently) but exponentially slower the closer to the theoretical endpoint, pH 8.3, you get, and in reality the endpoint is somewhere near 7.5 - 7.7.
(The reaction will also be slowed by a build-up of insoluble calcium phosphate on the surface of the limestone, but that's rarely a problem in real applications.)

But the point is that limestone "adjusts" towards a particular pH, not a particular conductivity, and has no effect at all on water with a pH higher than about 7.5 - 7.7.

So... if you want to maintain a pH of about 7.5, I would suggest to add limestone to the aquarium.

Another issue is howcome you get a drop from 7.5 to below 6 in just 3 days in an aquarium with an alkalinity of 4 dKH. Either whatever you use to measure pH is wrong, or something in the tank leaks vast amounts of acid.
I'm told tanks with extreme loads (e.g. koi or goldfish breeders) may experience pH crashes because the filter bacteria strip bicarbonate from the water faster than CO2 from the atmosphere can replace it, so if your tank has an extremely high bioload that might be what you're seeing. If so, limestone may react too slowly for your needs, and you may be better off dosing bicarbonate directly.

Also, of course, there's nothing stopping you from adding both limestone and bicarbonate.

[MatsP]

Mike,

Good explanation. But I doubt we need both versions of it. Tell me which of the two posts needs removing.

--
Mats

[Mike_Noren]

Bizarrely the second one is the wrong version. No idea how that happened.

[MatsP]

Well, the second one "is no more" - I can't explain how that would happen other than guessing it probably involves preview,browsers back-button and errors submitting the post in some combination(s).

--
Mats

[DaveT]

Thank you all for your input, much food for thought.

just to correct something, the tank isnt moving from 7.5 down to below 6, sorry if that wasnt clear, the tank water is dropping from approx , 6.5 - 6.6 down to my waterchange trigger lvl which is below 6. the rebuilt water that goes back into the tank is 7.8 and kh4, im pretty sure the kH is dropping off along with the pH, hence the need for another water change three days later. i havent been measuring the tank kH as i was under the impression that it was directly linked to the pH.

what i was hoping ot achieve with the coral sand was to create a buffered lvl of somewhere between 6 and 6.5 ideally, that would help to slow this process down a little, although from Mats input im not sure that adding the sand will have any effect in the long run. In which case i guess its just a case of buying and using more bicarb.

I must have understood the buffering malarky badly, i was thinking that x ammount of coral sand in the tank would stabilise the pH/kH at a certain lvl while adding more would increase the natural kH and pH of the tank system. my aim being to find a balance point where by the water parameters stayed how i wanted them much better than they do now.

Thanks again

Dave

[apistomaster]

What are the test results of your tap water before you run it through your RO filter?
It is often easier to simply dilute your tap water with RO to achieve your desired end results.
I don't find pH to very important in breeding Hypancistrus species but fairly soft water, 50-75 ppm TDS works well enough for my L260, L333 and Peckoltia sp L134. I dilute my tap water so it has a pH of 7.0.
I think you should tri a KH of 6 instead of 4. This will help maintain a more stable pH.
Sodium bicarbonate really isn't a very good way to try to control your pH.
Calcium carbonate works well to raise the KH so use Coral sand(aragonite). Limestone supplies the same chemical although generally at a much slower rate. That is, if for some reason simply diluting your tap water with RO water doesn't work for some reason. The nice part about diluting tap water is you retain a better balance of ions of all the minerals present in the tap water than simply adding specific chemicals.
I dilute my water 3 parts RO and 1 part tap water or 2 parts RO to 1 Tap water. My tap water has a KH of 6, GH 7, pH 7.4 and TDS of ~350 ppm. I change about 2/3 of my water twice a week. I do not care much which ratio I actually use so as long as it is within the ranges I stated. Frequent water changes generally only benefit and encourage regular spawning. If your pH is droping too low in one week you may have to much bioload or excessive feeding going on. That should be considered before fooling around with chemicals very much.

[DaveT]

Hiya Apisto.

unfortunately the local water supply is pretty dire, the water around here would naturally be soft and acidic, so to prevent corosion they pump it full of aluminium salts to up the pH, we end up with sky high pH yet soft water. I found this out after nearly loosing all my stock after changing water on all the tanks one saturday afternoon.

Ill see if i can get hold of calcium carbonite to substitute teh bicarb.

[DaveT]

sorry if my last post was cut off somewhat, i was trying to rush the post before setting off to work :/

so my plan of attack at the moment is to try and put some coral sand in the tank, (a little at a time to measure and changes in the water), in the mean time im adding extra bicarb to the water i put in during the water changes, im hoping that will gradually increase the kH to more stable lvl in the tank, the ammounts of bicarb being put in will hopefully be reduced with the introduction of the sand into the tanks but only time will tell on that score.

Thank you all for your help, its nice to be able to get good advice off you guys on here before running into the sunset on a wild idea

thanks again

Dave