Is brown algae on goldfish tank decor harmful to my goldfish?

Brown algae overgrowth can be due to high nitrates, too much light or overfeeding. Use a liquid home test kit or submit a water sample for testing. Most pet or fish stores will do this for free of for a small fee. If nitrates are over 40ppm, it can be decreased by performing partial water changes. Use only aged or conditioned water that is temperature matched to prevent stress or shock. You can also use a nitrate absorbing filter insert. The algae will need to be physically scrubbed from plants or rocks and can be scraped from glass. Rinse filter media using tank water NOT tap water. Limit light to 6 hours daily, 8 if you have live plants and do not over feed.

Thanks for reaching out. This problem is perplexing, but possibilities include fungal or bacterial overgrowths. A good cleaning might help to alleviate your problems. Continue to test water quality and correct problems. Sometimes the over-growth of anaerobic bacteria (those which grow in low or no oxygen conditions, at the bottom of the tank), can form strange formations of detritus. Submitting a sample to a lab might help determine an answer. Good luck.

Thanks for reaching out about Corn and including photos. This could be mineral deposits but is difficult to tell in the photos. Mold usually does not grow below the water level as needs oxygen. Clean the filter well. A sample of the material can be acquired and a veterinarian might be able to help by examining under the microscope. Good luck.

I would try to keep the algae to a minimum. Algae growth is caused by combination of too many nutritions (food left-overs) in the water, not enough current in the water and more than enough light. So you need to re-visit your husbandry to make sure everything is 100% correct. If the water current and lighting are correct then chances are you are over-feeding him. If you can reduce the left-overs you'll probably effectively remove the source of the algae growth. Hope this helps. Best wishes.

Sand substrate is always a problem as it promotes decay and anaerobic bacteria. If you need sand in a tank for a fish species (none of the ones you mentioned above actually need sand) you should not use it in the whole aquarium , but only in a small spot to accomodate the fish. Rust-colored spots on the glass and gravel are due to diatom algae. They likely were brought in with the silicates in the sand.Diatom algae need the silicates to make a shell they carry around with them. Remove the silicates, and the algae should die. Removing silicates can be done with a silicate and phosphate filter, or, in your case, I would remove the sand completely and refill your aquarium with washed gravel. Algae also need lots of nutrients, so if you overfeed your fish, algae will increase. Feed only what your fish eat in one minute, no more.

Looking at the photos, I agree that it doesn't look like the typical fungal infection. Generally you see multiple lesions and they tend to be fuzzy in appearance. I'm not sure what that is on the fin but it may be benign. I would recommend to call the pet store and tell them what you are seeing. Check to see if any of the other fish have become ill. Abnormalities on the fins can be fungal, bacterial or parasitic. There's also a change of a defect or injury. If the area is not really changing and your fish is acting normal, you may just monitor it. I hope this helps!

Check the water chemistry using a home test kit or submit a water sample for testing. The local Petco may do this for free or for a small fee. Aim for an absence (0 ppm) of ammonia and nitrites with nitrates at 20ppm or less. Perform partial water changes to stabilize chemistry and/or to improve water quality. Rinse the filter media in tank water, not tap water, and replace it. Use only conditioned water that is temperature matched to prevent stress or shock. To limit algae growth, maintain pristine water quality via filtration and regular water changes. If possible, turn up filter flow to keep water moving. If this stresses the fish though, do not do it. Do not overfeed and remove any uneaten food promptly. Limit lighting to 8 hours daily and closely monitor water temperature as well. All these can promote algae overgrowth.