Dropping PH and yellowish water

Hi, We have two fish tanks in our house that I maintain.
Mine is a 300+l community tank, with a cannister filter. Using Matrix and Purigen to keep the tank healthy and the water clear.
Tank re-setup after we moved home in December 2014 and everything is running well and the PH is stable.

The second tank is my father-in-law's tank. A 1.2m tank that house a couple of large goldfish, siamese algae eaters and one or two other fish.
There is no wood in this tank, but the water keeps getting a yellowish colour. Also the PH plumets from around 7 to in the 4's within 4-7 days. I use the same tap water for both tanks with prime.

I use a sera ph kit and sera kh kit to test the water.

In the past I used neutral regulator to get the PH back to 7.
I switched to using Alkaline Buffer to up the PH.
But after I get it up to 7 again, it just drops back down into the 4's.

Can anyone help? Any ideas? I really don't understand what can affect the water.
Can it be the large goldfish? The food? The plants?
Also is the yellowish colour of the water linked to problem?
The tank also uses a canister filter with matrix and purigen. I have cleaned the canister thoroughly but still have the same problem.

I would appreciate any ideas or suggestions.

PS. I'm looking for homes for the goldfish in the tank. They are getting really large and need a pond or larger tank.

 

Hi Viswolf,

How often do you do your water changes and how much do you change at a time ?

 

You do not say how many goldfish you keep and how big they are.
I would say overcrowding (as in too large and messy fish that produce lots of waste) and too seldom water changes (under the circumstances) is your problem.

 

Jeez,4 is really low...almost hard to believe.Are you sure you are testing correctly?The only way i could explain that is a combination of soft water,massive bio load,insufficient tank maintenance and water changes.

 

Well cape town water is soft. The yellow water is because of not doing enough maintenance on the tank. Dirty filter with dirty water. Overfeeding or over stocking. Still dont know how large these fish are and how many fish is in the tank. What size canister do you have on there

 

Agree with many in the above post. What media do you have in the filters besides the ones you mentioned.

 

Thanks for all the feedback.

I'm using an Eheim 2217 canister with sponge, filterfloss, Matrix and purigen. (Nothing else).

Attached a picture of the tank and fish.

The tank house:
7 goldfish / koi - the largest monster is 25cm long.
2 angels
1 pleco
2 clown loaches
2 siamese algae eaters.

I do a 25% water change once a month.

I check the PH of both tanks at the same time and the one stays at 7 and the other drops daily - so I don't think I'm testing incorrectly.

I'm looking for a good home for the goldfish. My father-in-law has had the big one for many years and we would like him to go to a good home.

 

Those goldfish look good to me and i think it's impressive you managed to grow them to that size in a fish tank.
But as you say...time to find a good new home or build a pond.
Once you've done that your problem will be solved.
Also i would do water changes weekly instead of once a month.

 

I would try doing a 25% water change every two weeks....see how it goes.

 

If your ph drops that much within a few days, I think you should do water changes accordingly.
Like min 25% per week, or even bigger ones every 4-5 days.
Doing 25% every 2 weeks isn't going to cut the mustard if your ph is down to 4 after 4-7 days, this means the fish spend more than 50% of the time in water with a ph of 4.