Green-ish water?

[Sandman1969]

My 30 gallon tank is home to one fan tailed goldfish & one koi. Each week, the water turns a slight green-ish color. I have 2 HOBs running of which one is an Aquaclear 500 and the other is a slightly modded Marineland Bio wheel filter. Slightly modded as instead of a cartridge, it uses floss & I have 2 pot scrubbers tucked in the bottom.
The Aquaclear has 2 bags of bio max along with the sponge & floss.
I do water changes each week.

Now, my 130 gallon, it never sees that color water as it is always 100% clear. It uses an XP 3 & a home-made 10 gallon tub filter. (10 gallon as in the size of the tub itself). It is loaded with lots of pot scrubbers, floss & sponge whereas the XP is pretty much a typical set up for it. That tank is home to one big, stunted ID shark & 2 baby IDs, 2 big common plecos & 4 oto cats.

My question is this, is the green water due to the fish themselves or a lacking filtration on the smaller tank? This tank does get some brown algae that I scrub off when I notice it. Would a Xp 1 be a better filter to use instead? I did see one on Kijiji for like $40/$50.

[nyleveiam]

I think it is the goldfish...they seem to be algae producers when I have mine in for the Winter, even with poor lighting.
I LOVE my UV sterilizer for keeping it under control!!  A new SunSun brand 15 watt is $35 -40 on Amazon...same as the filter!!!

[Sbenson11]

Is the 30 gal getting any direct sunlight?

Steve

[Biulu]

Goldfish produce a lot of waste which can quickly ensure an imbalance in the nutrients and thus algae.

I add potassium to the tank which has goldfish and I put in some potho and other plants.

Now even with sunlight coming from the window I only get brown algae.

[Sandman1969]

Steve, none at all.

So then it's nothing to do with filtration or lack thereof?

[Sbenson11]

Goldfish/Koi are dirty fish that produce a lot of waste that can add to Algae growth.

What kind of light do they get?

Just as a comparison, I have a 40 Gal in my Wife's office that has an Oranda, a fantail and 14 comets, some are now almost 4". it is way over crowded, but I am tight on space right now now and have no where else to put them. That being said I do a 50% water change every Sat and it is filtered with a single Aquaclear 50. All is good and no algae.

By the way, what's the long term plan for the Koi?

Steve

[Sandman1969]

They do not get direct sunlight as they are across from the balcony towards the front door on the 23rd floor.
I do half water changes each weekend as well.

As for the koi, don't know yet.

[Orlon11]

Goldfish are very great at creating algae - they're even used to culture green water in research labs!

Does the tank have a substrate? The water gets much more green in bare bottomed tanks.

[Sandman1969]

It has an inch or 2 of multi coloured pebbles on the bottom.