Toxic Algae?

HELP! 1 adult Cory cat, 1 adult Molly Both acting sick. Brown Algae all over everything. Lost 1 juvenile panda Cory for unknown reasons. Towards the end of completing nit cycle but recently changed filter. Temp is 76. Numbers in the pics. The one pic is of a quartz crystal that should be clear and is an orangish brown.

Brown algae - diatoms - are common in new tanks. The diatoms eventually go away.

Of more concern is the fish.
Do you know if you have hard or soft water? Mollies need hard water and if yours is soft that will contribute the the mollies ill health. Your water provider's website should have your hardness on it somewhere. You need a number and the unit as there are several units they could use.
Cories are soft water fish, and need to be in a shoal or at least 6. When are there not enough of them, they get stressed and stressed fish get sick more easily.

And both fish have been through a cycle, which weakens them and makes them more susceptible to illness.

Thank you. Our water reads “hard”-“very hard” on the strip tests we have. PH is a steady 8.2. We originally had 3 corys. The first died within a couple days, I believe from the stress of the ride home. Then we got a baby panda and it was doing great and growing, bright colors. Then after being fine for almost 2months, he became ill and died within a couple days. Our last Cory still looks healthy but his or her behavior has changed along with the Molly. Mainly they both seem to have gone from very social and curious to extremely shy (hiding a lot) and lethargic. Still eating but not overly interested as before even after fasting them a couple days. An experienced aquarist friend came over yesterday and suggested I need more and different substrate and suggested o turn my filter off. We have a Aquatech 20-40 and two strong bubblers going. He said with so few fish and the healthy have fern that it was turning jver the water to many times a day. We have it a try, turning it off, but left the two bubblers going for about 30 hours now. Water is a bit cloudy, fish came out to eat but still seem dodgy and fins straights up. So yeah....prob too much info but hopefully a bigger window into my fishy world. Would love more feedback. Thanks again.

What are your current readings for ammonia, nitrite and nitrate? What does (f) and (b) mean on your recent results? You had zero nitrates, then a small amount which could indicate a mini cycle, especially if your tank is immature (running for less than six months).

Changing your filter, then turning your filter off could be effecting the cycle. Read up on cycling in the beginners section.

Turn your filter back on. You need it running to maintain the beneficial bacteria. If you are worried that there is too much water movement turn the bubblers off.

Can you check your water suppliers website to get a number and unit for the GH and KH please. The test strips "hard/ very hard" are not specific enough and could be interpreted differently. As Essjay already said, the two fish require different GH.

Naughts said:

What are your current readings for ammonia, nitrite and nitrate? What does (f) and (b) mean on your recent results? You had zero nitrates, then a small amount which could indicate a mini cycle, especially if your tank is immature (running for less than six months).

Changing your filter, then turning your filter off could be effecting the cycle. Read up on cycling in the beginners section.

Turn your filter back on. You need it running to maintain the beneficial bacteria. If you are worried that there is too much water movement turn the bubblers off.

Can you check your water suppliers website to get a number and unit for the GH and KH please. The test strips "hard/ very hard" are not specific enough and could be interpreted differently. As Essjay already said, the two fish require different GH.

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Current Readings are the same as of right now. Am=.25 Ni =0 Na=5-10. The (f)=fry tank which is 5gal and the (b)= big tank which is 20 and is on week 9 of cycling. We turned the filter off b/c we believe it was turning the water over too much. The filter is for 20-40 gal. The fish seem much happier as of right now. I did order replacement cartridges for our original filter that came with the tank, an Aqueon quietflow 10.